CUBO A Mathematical Journal
Vol.21, No¯ 02, (15–40). August 2019

http: // dx. doi. org/ 10. 4067/ S0719-06462019000200015

Zk-Magic Labeling of Path Union of Graphs

P. Jeyanthi
1
K. Jeya Daisy

2
and Andrea Semaničová-Feňovč́ıková

3

1Research Centre, Department of Mathematics,

Govindammal Aditanar College for Women,

Tiruchendur 628215, Tamilnadu, India

jeyajeyanthi@rediffmail.com

2Department of Mathematics,

Holy Cross College, Nagercoil, Tamilnadu, India

jeyadaisy@yahoo.com

3Department of Applied Mathematics and Informatics,

Technical University, Košice, Slovak Republic

andrea.fenovcikova@tuke.sk

ABSTRACT

For any non-trivial Abelian group A under addition a graph G is said to be A-magic

if there exists a labeling f : E(G) → A − {0} such that, the vertex labeling f+ defined

as f+(v) =
∑

f(uv) taken over all edges uv incident at v is a constant. An A-magic

graph G is said to be Zk-magic graph if the group A is Zk, the group of integers modulo

k and these graphs are referred as k-magic graphs. In this paper we prove that the

graphs such as path union of cycle, generalized Petersen graph, shell, wheel, closed

helm, double wheel, flower, cylinder, total graph of a path, lotus inside a circle and

n-pan graph are Zk-magic graphs.

http://dx.doi.org/10.4067/S0719-06462019000200015


16 YP. Jeyanthi, K. Jeya Daisy and Andrea Semaničová-Feňovč́ıková CUBO
21, 2 (2019)

RESUMEN

Para cualquier grupo Abeliano no-trivial A bajo adición, un grafo G se dice A-mágico

si existe un etiquetado f : E(G) → A − {0} tal que el etiquetado de un vértice f+

definido como f+(v) =
∑

f(uv), tomado sobre todos los ejes uv incidentes en v, es

constante. Un grafo A-mágico G se dice Zk-mágico si el grupo A es Zk, el grupo de

enteros módulo k y estos se llaman grafos k-mágicos. En este paper demostramos que

los grafos tales como la unión por caminos de ciclos, grafos de Petersen generalizados,

concha, rueda, casco cerrado, rueda doble, flor, cilindro, el grafo total de un camino,

lotos dentro de un ćırculo y n-sartenes son todos grafos Zk-mágicos.

Keywords and Phrases: A-magic labeling, Zk-magic labeling, Zk-magic graph, generalized

Petersen graph, shell, wheel, closed helm, double wheel, flower, cylinder, total graph of a path,

lotus inside a circle, n-pan graph.

2010 AMS Mathematics Subject Classification: 05C78.



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Zk-Magic Labeling of Path Union of Graphs 17

1 Introduction

Graph labeling is currently an emerging area in the research of graph theory. A graph labeling

is an assignment of integers to vertices or edges or both subject to certain conditions. A detailed

survey was done by Gallian in [1]. If the labels of edges are distinct positive integers and for each

vertex v the sum of the labels of all edges incident with v is the same for every vertex v in the

given graph then the labeling is called a magic labeling. Sedláček [10] introduced the concept of

A-magic graphs. A graph with real-valued edge labeling such that distinct edges have distinct

non-negative labels and the sum of the labels of the edges incident to a particular vertex is same

for all vertices. Low and Lee [9] examined the A-magic property of the resulting graph obtained

from the product of two A-magic graphs. Shiu, Lam and Sun [12] proved that the product and

composition of A-magic graphs were also A-magic.

For any non-trivial Abelian group A under addition a graph G is said to be A-magic if there

exists a labeling f : E(G) → A−{0} such that, the vertex labeling f+ defined as f+(v) =
∑

f(uv)

taken over all edges uv incident at v is a constant. An A-magic graph G is said to be Zk-magic

graph if the group A is Zk, the group of integers modulo k. These Zk-magic graphs are referred

to as k-magic graphs. Shiu and Low [13] determined all positive integers k for which fans and

wheels have a Zk-magic labeling with a magic constant 0. Kavitha and Thirusangu [8] obtained

a Zk-magic labeling of two cycles with a common vertex. Motivated by the concept of A-magic

graph in [10] and the results in [9, 12, 13] Jeyanthi and Jeya Daisy [2, 3, 4, 5, 6, 7] proved that

some standard graphs admit Zk-magic labeling. We use the following definitions in the subsequent

section.

Definition 1.1. Let G1, G2, . . . , Gn, n ≥ 2, be copies of a graph G. Let vi ∈ V (Gi), i = 1, 2, . . . , n,

be the vertex corresponding to the vertex v ∈ V (G) in the ith copy of Gi. We denoted by P(n.G
v)

the graph obtained by adding the edge vivi+1, to Gi and Gi+1, 1 ≤ i ≤ n − 1, and we call P(n.G
v)

the path union of n copies of the graph G.

Note, that up to isomorphism, we obtain |V (G)| graphs P(n.Gv). This operation was defined

in [11].

Definition 1.2. A generalized Petersen graph P(n, m), n ≥ 3, 1 ≤ m < n
2
is a 3-regular graph

with the vertex set {ui, vi : i = 1, 2, . . . , n} and the edge set {uivi, uiui+1, vivi+m : i = 1, 2, . . . , n},

where the indices are taken over modulo n.

Definition 1.3. A shell graph Sn, n ≥ 4, is obtained by taking n − 3 concurrent chords in a cycle

Cn. The vertex at which all the chords are concurrent is called an apex.

Definition 1.4. A wheel graph Wn, n ≥ 3, is obtained by joining the vertices of a cycle Cn to an

extra vertex called the centre. The vertices of degree three are called rim vertices.



18 YP. Jeyanthi, K. Jeya Daisy and Andrea Semaničová-Feňovč́ıková CUBO
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Definition 1.5. A helm graph Hn, n ≥ 3, is obtained from a wheel Wn by adjoining a pendant

edge at each vertex of the wheel except the center.

Definition 1.6. A closed helm graph CHn, n ≥ 3, is obtained from a helm Hn by joining each

pendent vertex to form a cycle.

Definition 1.7. A double wheel graph DWn, n ≥ 3, is obtained by joining the vertices of two

cycles Cn to an extra vertex called the hub.

Definition 1.8. A flower graph Fln, n ≥ 3, is obtained from a helm Hn by joining each pendent

vertex to the central vertex of the helm.

Definition 1.9. A Cartesian product of a cycle Cn, n ≥ 3, and a path on two vertices is called a

cylinder graph Cn�P2.

Definition 1.10. A total graph T (G) is a graph with the vertex set V (G) ∪ E(G) in which two

vertices are adjacent whenever they are either adjacent or incident in G.

Definition 1.11. A lotus inside a circle LCn, n ≥ 3, is a graph obtained from a wheel Wn by

subdividing every edge forming the outer cycle and joining these new vertices to form a cycle.

Definition 1.12. An n-pan graph, n ≥ 3, is obtained by attaching a pendent edge to a vertex of a

cycle Cn.

2 Zk-Magic Labeling of Path Union of Graphs

In this section we prove that the graphs such as path union of cycle, generalized Petersen graph,

shell, wheel, closed helm, double wheel, flower, cylinder, total graph of a path, lotus inside a circle

and n-pan graph are Zk-magic graphs.

Let v be a vertex of a cycle Cr, r ≥ 3. According to the symmetry all P(n.C
v
r ) are isomorphic.

Thus we use the notation P(n.Cr).

Theorem 2.1. Let r ≥ 3 and n ≥ 2 be integers. The path union of a cycle P(n.Cr) is Zk-magic

for k ≥ 3 when r is odd.

Proof. Let the vertex set and the edge set of P(n.Cr) be V (P(n.Cr)) = {v
j
i : 1 ≤ i ≤ r, 1 ≤ j ≤ n}

and E(P(n.Cr)) = {v
j
i v

j
i+1 : 1 ≤ i ≤ r, 1 ≤ j ≤ n} ∪ {v

j
1v

j+1
1 : 1 ≤ j ≤ n − 1}, where the index i

is taken over modulo r.

Let a, k be positive integers, k > 2a. Thus k ≥ 3.



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Zk-Magic Labeling of Path Union of Graphs 19

For r is odd, we define an edge labeling f : E(P(n.Cr)) → Zk − {0} as follows:

f(v1i v
1
i+1) = f(v

n
i v

n
i+1) =

{

k − a, for i = 1, 3, . . . , r,

a, for i = 2, 4, . . . , r − 1,

f(v
j
i
v
j
i+1) =

{

k − 2a, for i = 1, 3, . . . , r, j = 2, 3, . . . , n − 1,

2a, for i = 2, 4, . . . , r − 1, j = 2, 3, . . . , n − 1,

f(v
j
1v

j+1
1 ) = 2a, for j = 1, 2, . . . , n − 1.

Then the induced vertex labeling f+ : V (P(n.Cr)) → Zk is f
+(v) ≡ 0 (mod k) for every vertex v

in V (P(n.Cr)).

An example of a Z10-magic labeling of P(4.C5) is shown in Figure 1.

b

b

b
b

2
2

8

88

b

b b

b

b
b

b

4
4

6

66
b b

b

b
b

b

4
4

6

66

b b

b

b
b

b

2
2

8

8 8

bb bbb

4 44

b

Figure 1: A Z10-magic labeling of P(4.C5).

Up to isomorphism there are two graphs obtained by attaching n copies of a generalized

Petersen graph P(r, m), r ≥ 3, 1 ≤ m ≤ r−1
2

to a path Pn to get a graph P(n.P(r, m)
v). We deal

with the case when v is a vertex in the outer polygon of P(r, m).

Theorem 2.2. Let r ≥ 3, m ≤ r−1
2

and n ≥ 2 be positive integers. The path union of a generalized

Petersen graph P(n.P(r, m)v), where v is a vertex in the outer polygon of P(r, m), is Zk-magic

for k ≥ 5 when r is odd.

Proof. Let the vertex set and the edge set of P(n.P(r, m)v) be V (P(n.P(r, m)v)) = {u
j
i, v

j
i : 1 ≤

i ≤ r, 1 ≤ j ≤ n} and E(P(n.P(r, m)v)) = {u
j
iv

j
i : 1 ≤ i ≤ r, 1 ≤ j ≤ n} ∪ {u

j
iu

j
i+1 : 1 ≤ i ≤ r, 1 ≤

j ≤ n} ∪ {u
j
1u

j+1
1 : 1 ≤ j ≤ n − 1} ∪ {v

j
i v

j
i+m : 1 ≤ i ≤ r, 1 ≤ j ≤ n}, where the index i is taken

over modulo r.

Let a, k be positive integers, k > 4a. Thus k ≥ 5.



20 YP. Jeyanthi, K. Jeya Daisy and Andrea Semaničová-Feňovč́ıková CUBO
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Define an edge labeling f : E(P(n.P(r, m)v)) → Zk − {0} as follows:

f(v
j
i v

j
i+m) = a, for i = 1, 2, . . . , r, j = 1, 2, . . . , n − 1,

f(u
j
iv

j
i ) = k − 2a, for i = 1, 2, . . . , r, j = 1, 2, . . . , n − 1,

f(u1i u
1
i+1) =

{

k − a, for i = 1, 3, . . . , r,

3a, for i = 2, 4, . . . , r − 1,

f(u
j
iu

j
i+1) = a, for i = 1, 2, . . . , r, j = 2, 3, . . . , n − 1,

f(vni v
n
i+m) =

{

k − a, for n is odd,

a, for n is even,

f(uni v
n
i ) =

{

2a, for n is odd,

k − 2a, for n is even,

f(uni u
n
i+1) =



















a, for i = 1, 3, . . . , r and n is odd,

k − 3a, for i = 2, 4, . . . , r − 1 and n is odd,

k − a, for i = 1, 3, . . . , r and n is even,

3a, for i = 2, 4, . . . , r − 1 and n is even,

f(u
j
1u

j+1
1 ) =

{

4a, for j = 1, 3, . . . and j ≤ n − 1,

k − 4a, for j = 2, 4, . . . and j ≤ n − 1.

Then the induced vertex labeling f+ : V (P(n.P(r, m)v)) → Zk is f
+(u) ≡ 0 (mod k) for all

u ∈ V (P(n.P(r, m)v)). Thus V (P(n.P(r, m)v)) is a Zk-magic graph.

An example of a Z15-magic labeling of P(5.P(5, 2)
v) is shown in Figure 2.

b

b
b

b

b

b

b
b

b

b

2

2

22

2

11

13
11

11

11

11

13

13

6

6

b

b
b

b

b

b

b
b

b

b

2

2

22

2

11

11

11

11

11

b

b
b

b

b

b

b
b

b

b
2

8

2

4

13 9

13
b

b
b

b

b

b

b
b

b

b

2

2

22

2

11

11

11

11

11

b

b
b

b

b

b

b
b

b

b

2

2

22

2

11

11

11

11

11

b b b b b
2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

13

13 13

4

4

4

4

2

9

8 77

Figure 2: A Z15-magic labeling of P(5.P(5, 2)
v).

Theorem 2.3. Let r ≥ 4 and n ≥ 2 be positive integers. The path union of a shell graph P(n.Svr ),

where v ∈ V (Sr) is the vertex of degree r − 1, is Zk-magic for k ≥ 2r − 3 when r is odd and for

k ≥ r − 1 when k is even.

Proof. Let the vertex set and the edge set of P(n.Svr ) be V (P(n.S
v
r )) = {v

j
i : 1 ≤ i ≤ r, 1 ≤ j ≤ n}

and E(P(n.Svr )) = {v
j
i v

j
i+1 : 1 ≤ i ≤ r, 1 ≤ j ≤ n} ∪ {v

j
1v

j
i : 3 ≤ i ≤ r, 1 ≤ j ≤ n} ∪ {v

j
1v

j+1
1 : 1 ≤

j ≤ n − 1} with the index i taken over modulo r.



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Zk-Magic Labeling of Path Union of Graphs 21

We consider the following two cases according to the parity of r.

Case (i): when r is odd.

Let a, k be positive integers, k > 2(r − 2)a. Thus k ≥ 2r − 3.

Define an edge labeling f : E(P(n.Svr )) → Zk − {0} as follows:

f(v11v
1
i ) = 2a, for i = 3, 4, . . . , r − 1,

f(v11v
1
2) = f(v

1
rv

1
1) = a,

f(v1i v
1
i+1) = k − a, for i = 2, 3, . . . , r − 1,

f(v
j
1v

j+1
1 ) =

{

k − 2a(r − 2), for j = 1, 3, . . . and j ≤ n − 1,

2a(r − 2), for j = 2, 4, . . . and j ≤ n − 1,

f(v
j
1v

j
i ) = a, for i = 3, 4, . . . , r − 1, j = 2, 3, . . . , n − 1,

f(v
j
i
v
j
i+1) =

{

(r−3)a
2

, for i = 2, 4, . . . , r − 1, j = 2, 3, . . . , n − 1,

k −
(r−1)a

2
, for i = 3, 5, . . . , r − 2, j = 2, 3, . . . , n − 1,

f(v
j
1v

j
2) = f(v

j
rv

j
1) = k −

(r−3)a
2

, for j = 2, 3, . . . , n − 1,

f(vn1 v
n
i ) =

{

k − 2a, for i = 3, 4, . . . , r − 1 and n is odd,

2a, for i = 3, 4, . . . , r − 1 and n is even,

f(vn1 v
n
2 ) = f(v

n
r v

n
1 ) =

{

k − a, for n is odd,

a, for n is even,

f(vni v
n
i+1) =

{

a, for i = 2, 3, . . . , r − 1 and n is odd,

k − a, for i = 2, 3, . . . , r − 1 and n is even.

Then the induced vertex labeling f+ : V (p(n.Svr )) → Zk is f
+(u) ≡ 0 (mod k) for all u ∈

V (P(n.Svr )).

Case (ii): when r is even.

Let a, k be positive integers, k > (r − 2)a. Thus k ≥ r − 1.



22 YP. Jeyanthi, K. Jeya Daisy and Andrea Semaničová-Feňovč́ıková CUBO
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Define an edge labeling f : E(P(n.Svr )) → Zk − {0} in the following way.

f(v11v
1
i ) = a, for i = 3, 4, . . . , r − 1,

f(v11v
1
2) = k − a,

f(v1rv
1
1) = 2a,

f(v1i v
1
i+1) =

{

a, for i = 2, 4, . . . , r − 2,

k − 2a, for i = 3, 5, . . . , r − 1,

f(v
j
1v

j+1
1 ) =

{

k − a(r − 2), for j = 1, 3, . . . and j ≤ n − 1,

a(r − 2), for j = 2, 4, . . . and j ≤ n − 1,

f(v
j
1v

j
i ) =

k
2
, for i = 3, 4, . . . , r − 1, j = 2, 3, . . . , n − 1,

f(v
j
i v

j
i+1) =











3k
4
, for i = 2, 3, . . . , r − 1, j = 2, 3, . . . , n − 1 and k ≡ 0 (mod 4),

3k+2
4

, for i = 2, 4, . . . , r − 2, j = 2, 3, . . . , n − 1 and k ≡ 2 (mod 4),
3k−2

4
, for i = 3, 5, . . . , r − 1, j = 2, 3, . . . , n − 1 and k ≡ 2 (mod 4),

f(v
j
1v

j
2) =

{

k
4
, for j = 2, 3, . . . , n − 1 and k ≡ 0 (mod 4),

k−2
4

, for j = 2, 3, . . . , n − 1 and k ≡ 2 (mod 4),

f(vjrv
j
1) =

{

k
4
, for j = 2, 3, . . . , n − 1 and k ≡ 0 (mod 4),

k+2
4

, for j = 2, 3, . . . , n − 1 and k ≡ 2 (mod 4),

f(vn1 v
n
i ) =

{

k − a, for i = 3, 4, . . . , r − 1 and n is odd,

a, for i = 3, 4, . . . , r − 1 and n is even,

f(vn1 v
n
2 ) =

{

a, for n is odd,

k − a, for n is even,

f(vnr v
n
1 ) =

{

k − 2a, for n is odd,

2a, for n is even,

f(vni v
n
i+1) =



















k − a, for i = 2, 4, . . . , r − 2 and n is odd

2a, for i = 3, 5, . . . , r − 1 and n is odd,

a, for i = 2, 4, . . . , r − 2 and n is even,

k − 2a, for i = 3, 5, . . . , r − 1 and n is even.

Then the induced vertex labeling f+ : V (P(n.Svr )) → Zk is f
+(u) ≡ 0 (mod k) for all u ∈

V (P(n.Svr )). Thus P(n.S
v
r ) is a Zk-magic graph for r is even.

An example of a Z11-magic labeling of P(3.S
v
7 ) is shown in Figure 3.

According to the symmetry of wheels there exist two non isomorphic graphs P(n.W vr ). We

deal with the case when v is a rim vertex, that is a vertex of degree three in Wr.

Theorem 2.4. Let r ≥ 4 and n ≥ 2 be integers. The path union of a wheel graph P(n.W vr ), where

v ∈ V (Wr) is a vertex of degree 3, is Zk-magic for k ≥ r when r is odd and for k ≥ 2r − 1 when r



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Zk-Magic Labeling of Path Union of Graphs 23

b

b

b
b

b

b

1

1

1

1

1

1010

b

b

b
b

b

b

1

1
1

1 2
2

2

9

8

9

8

b

b

b
b

b

b

2
2

2 2

1 1

10

10

10

10

10

b b b

9

9 9

9

1 10

Figure 3: A Z11-magic labeling of P(3.S
v
7 ).

is even.

Proof. Let the vertex set and the edge set of P(n.W vr ) be V (P(n.W
v
r )) = {wj, v

j
i : 1 ≤ i ≤ r, 1 ≤

j ≤ n} and E(P(n.W vr )) = {v
j
i v

j
i+1 : 1 ≤ i ≤ r, 1 ≤ j ≤ n} ∪ {wjv

j
i : 1 ≤ i ≤ r, 1 ≤ j ≤

n} ∪ {u
j
1u

j+1
1 : 1 ≤ j ≤ n − 1}, where the index i is taken over modulo r.

We consider the following two cases according to the parity of r.

Case (i): when r is odd.

Let a, k be positive integers, k > (r − 1)a. This implies k ≥ r.

Define an edge labeling f : E(P(n.W vr )) → Zk − {0} as follows:

f(wjv
j
i ) = a, for i = 2, 3, . . . , r, j = 1, 2, . . . , n − 1,

f(wjv
j
1) = k − (r − 1)a, for j = 1, 2, . . . , n − 1,

f(v1i v
1
i+1) =

{

a, for i = 1, 3, . . . , r,

k − 2a, for i = 2, 4, . . . , r − 1,

f(v
j
i v

j
i+1) =

{

(r−1)a
2

, for i = 1, 3, . . . , r, j = 2, 3, . . . , n − 1,

k −
(r+1)a

2
, for i = 2, 4, . . . , r − 1, j = 2, 3, . . . , n − 1,

f(wnv
n
1 ) =

{

(r − 1)a, for n is odd,

k − (r − 1)a, for n is even,

f(wnv
n
i ) =

{

k − a, for i = 2, 3, . . . , r and n is odd,

a, for i = 2, 3, . . . , r and n is even,

f(vni v
n
i+1) =



















k − a, for i = 1, 3, . . . , r and n is odd,

2a, for i = 2, 4, . . . , r − 1 and n is odd,

a, for i = 1, 3, . . . , r and n is even,

k − 2a, for i = 2, 4, . . . , r − 1 and n is even,

f(v
j
1v

j+1
1 ) =

{

a(r − 3), for j = 1, 3, . . . and j ≤ n − 1,

k − a(r − 3), for j = 2, 4, . . . and j ≤ n − 1.

This means that for the induced vertex labeling f+ : V (P(n.W vr )) → Zk is f
+(u) ≡ 0 (mod k) for



24 YP. Jeyanthi, K. Jeya Daisy and Andrea Semaničová-Feňovč́ıková CUBO
21, 2 (2019)

all u ∈ V (P(n.W vr )).

Case (ii): when r is even.

Let a, k be positive integers, k > 2(r − 1)a.

Define an edge labeling f : E(P(n.W vr )) → Zk − {0} in the following way.

f(w1v
j
1) = f(wnv

n
1 ) = k − (r − 1)a,

f(w1v
1
i ) = f(wnv

n
i ) = a, for i = 2, 3, . . . , r,

f(v1i v
1
i+1) = f(v

n
i v

n
i+1) =

{

a, for i = 1, 3, . . . , r − 1,

k − 2a, for i = 2, 4, . . . , r,

f(wjv
j
1) = k − 2(r − 1)a, for j = 2, 3, . . . , n − 1,

f(wjv
j
i ) = 2a, for i = 2, 3, . . . , r, j = 2, 3, . . . , n − 1,

f(v
j
i v

j
i+1) = k − a, for i = 1, 2, . . . , r, j = 2, 3, . . . , n − 1,

f(v
j
1v

j+1
1 ) = ra, for j = 1, 2, . . . , n − 1.

Then the induced vertex labeling f+ : V (P(n.W vr )) → Zk is f
+(u) ≡ 0 (mod k) for all u ∈

V (P(n.W vr )). Hence f
+ is constant that means P(n.W vr ) admits a Zk-magic labeling.

An example of a Z12-magic labeling of P(3.W
v
6 ) is shown in Figure 4.

b

b

b

b

b

b

b
2

2

2
2

2

2
11

11 11

11

1111

b

b

b

b

b

b

b

1

7
1

1

1

1

1
1

1

10

10

10

b

b

b

b

b

b

b

1

7

1

1

1

1

1
1

1

10

10

10

b b b

66

Figure 4: A Z12-magic labeling of P(3.W
v
6 ).

In the next theorem we deal with the path union of a closed helm graph P(n.CHvr ), where v

is a vertex of degree three in CHr.

Theorem 2.5. Let r ≥ 4 and n ≥ 2 be integers. The path union of a closed helm graph P(n.CHvr ),

where v is a vertex of degree 3 in CHr, is Zk-magic for k ≥ r when r is odd and for even k ≥ r

when r is even.

Proof. Let the vertex set and the edge set of P(n.CHvr ) be V (P(n.CH
v
r )) = {wj, v

j
i , u

j
i : 1 ≤ i ≤

r, 1 ≤ j ≤ n} and E(P(n.CHvr )) = {v
j
i v

j
i+1 : 1 ≤ i ≤ r, 1 ≤ j ≤ n} ∪ {u

j
iu

j
i+1 : 1 ≤ i ≤ r, 1 ≤ j ≤

n} ∪ {wjv
j
i : 1 ≤ i ≤ r, 1 ≤ j ≤ n} ∪ {v

j
i u

j
i : 1 ≤ i ≤ r, 1 ≤ j ≤ n} ∪ {u

j
1u

j+1
1 : 1 ≤ j ≤ n − 1},

where the index i is taken over modulo r.



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Zk-Magic Labeling of Path Union of Graphs 25

Case (i): when r is odd.

Let a, k be positive integers, k > (r − 1)a. Thus k ≥ r.

Define an edge labeling f : E(P(n.CHvr )) → Zk − {0} as follows:

f(wjv
j
1) = k − (r − 1)a, for j = 1, 2, . . . , n − 1,

f(wjv
j
i ) = a, for i = 2, 3, . . . , r, j = 1, 2, . . . , n − 1,

f(v
j
i v

j
i+1) =

{

(r − 1)a, for i = 1, 3, . . . , r, j = 1, 2, . . . , n − 1,

k − (r − 1)a, for i = 2, 4, . . . , r − 1, j = 1, 2, . . . , n − 1,

f(u1i u
1
i+1) =

{

(r − 1)a, for i = 1, 3, . . . , r,

k − (r − 2)a, for i = 2, 4, . . . , r − 1,

f(v
j
i u

j
i ) = k − a, for i = 2, 3, . . . , r, j = 1, 2, . . . , n − 1,

f(v
j
1u

j
1) = k − (r − 1)a, for j = 1, 2, . . . , n − 1,

f(u
j
i
u
j
i+1) =

{

(r−1)a
2

, for i = 1, 3, . . . , r, j = 2, 3, . . . , n − 1,

k −
(r−3)a

2
, for i = 2, 4, . . . , r − 1, j = 2, 3, . . . , n − 1,

f(wnv
n
1 ) =

{

(r − 1)a, for n is odd,

k − (r − 1)a, for n is even,

f(wnv
n
i ) =,

{

k − a, for i = 2, 3, . . . , r and n is odd,

a, for i = 2, 3, . . . , r and n is even,

f(vn1 u
n
1 ) =

{

(r − 1), for n is odd,

k − (r − 1)a, for n is even,

f(vni u
n
i ) =

{

a, for i = 2, 3, . . . , r and n is odd,

k − a, for i = 2, 3, . . . , r and n is even,

f(vni v
n
i+1) =



















k − (r − 1)a, for i = 1, 3, . . . , r and n is odd,

(r − 1)a, for i = 2, 4, . . . , r − 1 and n is odd,

(r − 1)a, for i = 1, 3, . . . , r and n is even,

k − (r − 1)a, for i = 2, 4, . . . , r − 1 and n is even,

f(uni u
n
i+1) =



















k − (r − 1)a, for i = 1, 3, . . . , r and n is odd,

(r − 2)a, for i = 2, 4, . . . , r − 1 and n is odd,

(r − 1)a, for i = 1, 3, . . . , r and n is even,

k − (r − 2)a, for i = 2, 4, . . . , r − 1 and n is even,

f(u
j
1u

j+1
1 ) =

{

k − (r − 1)a, for j = 1, 3, . . . and j ≤ n − 1,

(r − 1)a, for j = 2, 4, . . . and j ≤ n − 1.

Then the induced vertex labeling f+ : V (P(n.CHvr )) → Zk is f
+(u) ≡ 0 (mod k) for all u ∈

V (P(n.CHvr )).



26 YP. Jeyanthi, K. Jeya Daisy and Andrea Semaničová-Feňovč́ıková CUBO
21, 2 (2019)

Case (ii): when r is even.

Let a be a positive integer and k > (r − 2)a be an even integer. Thus k ≥ r.

Define an edge labeling f : E(P(n.CHvr )) → Zk − {0} such that

f(w1v
1
1) = k − (r − 1)a,

f(w1v
1
i ) = a, for i = 2, 3, . . . , r,

f(v1i v
1
i+1) =

{

(r − 1)a, for i = 1, 3, . . . , r − 1,

k − (r − 1)a, for i = 2, 4, . . . , r,

f(u1i u
1
i+1) =

{

(r − 1)a, for i = 1, 3, . . . , r − 1,

k − (r − 2)a, for i = 2, 4, . . . , r − 1,

f(v11u
1
1) = (r − 1)a,

f(v1i u
1
i ) = k − a, for i = 2, 3, . . . , r,

f(wjv
j
i ) = f(v

j
i u

j
i ) = f(v

j
i v

j
i+1) =

k
2
, for i = 1, 2, . . . , r, j = 2, 3, . . . , n − 1,

f(u
j
i u

j
i+1) =











k
4
, for i = 1, 2, . . . , r, j = 2, 3, . . . , n − 1 and k ≡ 0 (mod 4),

k−2
4

, for i = 1, 3, . . . , r − 1, j = 2, 3, . . . , n − 1 and k ≡ 2 (mod 4),
k+2
4

, for i = 2, 4, . . . , r, j = 2, 3, . . . , n − 1 and k ≡ 2 (mod 4),

f(wnv
n
1 ) =

{

(r − 1)a, for n is odd,

k − (r − 1)a, for n is even,

f(wnv
n
i ) =

{

k − a, for i = 2, 3, . . . , r and n is odd,

a, for i = 2, 3, . . . , r and n is even,

f(vn1 u
n
1 ) =

{

k − (r − 1)a, for n is odd,

(r − 1)a, for n is even,

f(vni u
n
i ) =

{

a, for i = 2, 3, . . . , r and n is odd,

k − a, for i = 2, 3, . . . , r and n is even,

f(vni v
n
i+1) =



















k − (r − 1)a, for i = 1, 3, . . . , r − 1 and n is odd,

(r − 1)a, for i = 2, 4, . . . , r and n is odd,

(r − 1)a, for i = 1, 3, . . . , r − 1 and n is even,

k − (r − 1)a, for i = 2, 4, . . . , r and n is even,

f(uni u
n
i+1) =



















k − (r − 1)a, for i = 1, 3, . . . , r − 1 and n is odd,

(r − 2)a, for i = 2, 4, . . . , r and n is odd,

(r − 1)a, for i = 1, 3, . . . , r − 1 and n is even,

k − (r − 2)a, for i = 2, 4, . . . , r and n is even,

f(u
j
1u

j+1
1 ) =

{

k − ra, for j = 1, 3, . . . and j ≤ n − 1,

ra, for j = 2, 4, . . . and j ≤ n − 1.

Then the induced vertex labeling f+ : V (P(n.CHvr )) → Zk is f
+(u) ≡ 0 (mod k) for all u ∈



CUBO
21, 2 (2019)

Zk-Magic Labeling of Path Union of Graphs 27

V (P(n.CHvr )). Hence f
+ is constant equal to 0 (mod k). Therefore P(n.CHvr ) is a Zk-magic

graph.

An example of a Z6-magic labeling of P(3.CH
v
6 ) is shown in Figure 5.

b

b

b

b

b

b

bb

b

b

b

b

b

b

b

b

b

b

b

bb

b

b

b

b

b

b

b

b

b

b

b

bb

b

b

b
1

11
7

1

1
1

1

5

5

5

5

5

5

11

11

11
7

7

7

8

8

8

b

b

11

5

b b

1

7

5

8

11

6

3

1

1

1

1

6

6
6

6

6

6

6

66

6

6

6

6

6

6
6

6

5

5

5

5

5
8

8

11

11

11

11

7

7

7

5

3

3

3
3

3

6 6

Figure 5: A Z12-magic labeling of P(3.CH
v
6 ).

Theorem 2.6. Let r ≥ 3 and n ≥ 2 be integers. The path union of a double wheel graph

P(n.DW vr ), where v ∈ V (DWr) is a vertex of degree 3, is Zk-magic for k ≥ 5 when r is odd.

Proof. Let the vertex set and the edge set of C(n.DW vr ) be V (P(n.DW
v
r )) = {vj, v

j
i , u

j
i : 1 ≤ i ≤

r, 1 ≤ j ≤ n} and E(P(n.DW vr )) = {vjv
j
i , vju

j
i : 1 ≤ i ≤ r, 1 ≤ j ≤ n} ∪ {v

j
i v

j
i+1 : 1 ≤ i ≤ r, 1 ≤

j ≤ n} ∪{u
j
iu

j
i+1 : 1 ≤ i ≤ r, 1 ≤ j ≤ n} ∪{u

j
1u

j+1
1 : 1 ≤ j ≤ n− 1} with index i taken over modulo

r.

Let a, k be positive integers, k > 4a. Thus k ≥ 5.



28 YP. Jeyanthi, K. Jeya Daisy and Andrea Semaničová-Feňovč́ıková CUBO
21, 2 (2019)

For r is odd we define an edge labeling f : E(P(n.DW vr )) → Zk − {0} as follows:

f(vjv
j
i ) = 2a, for i = 1, 2, . . . , r, j = 1, 2, . . . , n − 1,

f(vju
j
i
) = k − 2a, for i = 1, 2, . . . , r, j = 1, 2, . . . , n − 1,

f(v
j
i v

j
i+1) = k − a, for i = 1, 2, . . . , r, j = 1, 2, . . . , n − 1,

f(u1i u
1
i+1) =

{

k − a, for i = 1, 3, . . . , r,

3a, for i = 2, 4, . . . , r − 1,

f(u
j
i u

j
i+1) = a, for i = 1, 2, . . . , r, j = 2, 3, . . . , n − 1,

f(vnv
n
i ) =

{

k − 2a, for i = 1, 2, . . . , r and n is odd,

2a, for i = 1, 2, . . . , r and n is even,

f(vnu
n
i ) =

{

2a, for i = 1, 2, . . . , r and n is odd,

k − 2a, for i = 1, 2, . . . , r and n is even,

f(vni v
n
i+1) =

{

a, for i = 1, 2, . . . , r − 1 and n is odd,

k − a, for i = 1, 2, . . . , r − 1 and n is even,

f(vnr v
n
1 ) =

{

a, for n is odd,

k − a, for n is even,

f(uni u
n
i+1) =



















a, for i = 1, 3, . . . , r and n is odd,

k − 3a, for i = 2, 4, . . . , r − 1 and n is odd,

k − a, for i = 1, 3, . . . , r and n is even,

3a, for i = 2, 4, . . . , r − 1 and n is even,

f(u
j
1u

j+1
1 ) =

{

4a, for j = 1, 3, . . . and j ≤ n − 1,

k − 4a, for j = 2, 4, . . . and j ≤ n − 1.

Then the induced vertex labeling f+ : V (P(n.DW vr )) → Zk is f
+(u) ≡ 0 (mod k) for all u ∈

V (P(n.DW vr )).

An example of a Z7-magic labeling of P(3.DW
v
7 ) is shown in Figure 6.

Theorem 2.7. Let r ≥ 3 and n ≥ 2 be positive integers. The path union of a flower graph

P(n.Flvr), where v ∈ V (Flr) is the vertex of degree 4, is Zk-magic for k ≥ 5 when r is odd and for

k ≥ 3 when k is even.

Proof. Let the vertex set and the edge set of P(n.Flvr) be V (P(n.Fl
v
r )) = {wj, v

j
i , u

j
i : 1 ≤ i ≤

r, 1 ≤ j ≤ n} and E(P(n.Flvr)) = {wjv
j
i : 1 ≤ i ≤ r, 1 ≤ j ≤ n} ∪ {v

j
i u

j
i : 1 ≤ i ≤ r, 1 ≤ j ≤

n} ∪ {wju
j
i : 1 ≤ i ≤ r, 1 ≤ j ≤ n} ∪ {v

j
i v

j
i+1 : 1 ≤ i ≤ r, 1 ≤ j ≤ n} ∪ {v

j
1v

j+1
1 : 1 ≤ j ≤ n − 1},

with index i taken over modulo r.

Case (i): when r is odd.



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21, 2 (2019)

Zk-Magic Labeling of Path Union of Graphs 29

b

2

3

5

6

2

2

2

2

2

2

6

6

6

6
6

6

5

5

5

5

5

5

6

6
6

6

3

3

b 4

b

2

5

6

2

2

2

2

2

2

6

6

6

6
6

6

5

5

5

5

5

5

1

11

1

1
1

1

b

2

52

2

2

2

2

2

1

5

5

5

5

5

5

b

1

1

1
1

1

1

1

1 1

1

4

4

4

3b

b

b

bb

b

b b

b

b

b

b

b

b

b

b

bb

b

b b

b

b

b

b

b

b b
b

b

bb

b

b
b

b

b

b

b

b

Figure 6: A Z7-magic labeling of P(3.DW
v
7 ).

Let a, k be positive integers, k > 4a. This means k ≥ 5.

Define an edge labeling f : E(P(n.Flvr)) → Zk − {0} as follows:

f(wjv
j
i ) = f(v

j
i u

j
i ) = a, for i = 1, 2, . . . , r, j = 1, 2, . . . , n − 1,

f(u
j
i wj) = k − a, for i = 1, 2, . . . , r, j = 1, 2, . . . , n − 1,

f(v1i v
1
i+1) =

{

a, for i = 1, 3, . . . , r,

k − 3a, for i = 2, 4, . . . , r − 1,

f(v
j
i v

j
i+1) = k − a, for i = 1, 2, . . . , r, j = 2, 3, . . . , n − 1,

f(wnv
n
i ) = f(v

n
i u

n
i ) =

{

k − a, for i = 1, 2, . . . , r and n is odd,

a, for i = 1, 2, . . . , r and n is even,

f(uni wn) =

{

a, for i = 1, 2, . . . , r and n is odd,

k − a, for i = 1, 2, . . . , r and n is even,

f(vni v
n
i+1) =



















k − a, for i = 1, 3, . . . , r and n is odd,

3a, for i = 2, 4, . . . , r − 1 and n is odd,

a, for i = 1, 3, . . . , r and n is even,

k − 3a, for i = 2, 4, . . . , r − 1 and n is even,

f(v
j
1v

j+1
1 ) =

{

k − 4a, for j = 1, 3, . . . and j ≤ n − 1,

4a, for j = 2, 4, . . . and j ≤ n − 1.

Then the induced vertex labeling f+ : V (P(n.Flvr)) → Zk is f
+(u) ≡ 0 (mod k) for all u ∈

V (P(n.Flvr)).

Case (ii): when r is even.

Let a, k be positive integers, k > 2a. Thus k ≥ 3.



30 YP. Jeyanthi, K. Jeya Daisy and Andrea Semaničová-Feňovč́ıková CUBO
21, 2 (2019)

Define an edge labeling f : E(P(n.Flvr)) → Zk − {0} as follows:

f(w1v
1
1) = f(v

1
1u

1
1) = 2a,

f(u11w1) = k − 2a,

f(v
j
i v

j
i+1) = k − a, for i = 1, 2, . . . , r, j = 2, 3, . . . , n − 1,

f(wjv
j
i ) = f(v

j
i u

j
i ) = a, for i = 2, 3, . . . , r, j = 1, 2, . . . , n − 1,

f(wju
j
i) = k − a, for i = 2, 3, . . . , r, j = 1, 2, . . . , n − 1,

f(wnv
n
1 ) = f(v

n
1 u

n
1 ) =

{

k − 2a, for n is odd,

2a, for n is even,

f(wnu
n
1 ) =

{

2a, for n is odd,

k − 2a, for n is even,

f(wnv
n
i ) = f(v

n
i u

n
i ) =

{

k − a, for i = 2, 3, . . . , r and n is odd,

a, for i = 2, 3, . . . , r and n is even,

f(wnu
n
i ) =

{

a, for i = 2, 3, . . . , r and n is odd,

k − a, for i = 2, 3, . . . , r and n is even,

f(vni v
n
i+1) =

{

a, for i = 1, 2, . . . , r and n is odd,

k − a, for i = 1, 2, . . . , r and n is even,

f(v
j
1v

j+1
1 ) =

{

k − 2a, for j = 1, 3, . . . and j ≤ n − 1,

2a, for j = 2, 4, . . . and j ≤ n − 1.

The induced vertex labeling f+ : V (P(n.Flvr)) → Zk is f
+(u) ≡ 0 (mod k) for all u ∈ V (P(n.Flvr)).

An example of a Z10-magic labeling of P(4.Fl
v
3) is shown in Figure 7.

b

b

2
2

2

2

8

8

b

b b

b

2

8

8

8

8

2

b

b

b

b

2
2

2

2

8
8

b

b b

b

2

8

8

8
2
b

b

8

b

b

2 2

2

2

4

8
8

2

b

b

b

2
8

2

b

2

b

b

b

b

2

2

2

2 4

8

82

b

b b

b

2

8

2

b

b

2
2 8 2

Figure 7: A Z10-magic labeling of P(4.Fl
v
3).

Let v be a vertex of a cylinder graph Cr�P2, r ≥ 3. According to the symmetry all

P(n.(Cr�P2)
v) are isomorphic. Thus we use the notation P(n.(Cr�P2)).

Theorem 2.8. Let r ≥ 3, n ≥ 2 be integers. The path union of a cylinder graph P(n.(Cr�P2)) is

Zk-magic for k ≥ 5 when r is odd.



CUBO
21, 2 (2019)

Zk-Magic Labeling of Path Union of Graphs 31

Proof. Let the vertex set and the edge set of P(n.(Cr�P2)) be V (P(n.(Cr�P2))) = {v
j
i , u

j
i : 1 ≤

i ≤ r, 1 ≤ j ≤ n} and E(P(n.(Cr�P2))) = {u
j
iv

j
i : 1 ≤ i ≤ r, 1 ≤ j ≤ n} ∪ {u

j
iu

j
i+1 : 1 ≤ i ≤ r, 1 ≤

j ≤ n} ∪ {v
j
i v

j
i+1 : 1 ≤ i ≤ r, 1 ≤ j ≤ n} ∪ {u

j
1u

j+1
1 : 1 ≤ j ≤ n − 1}, with index i taken over

modulo r.

Let a, k be positive integers, k > 4a. Thus k ≥ 5.

For r odd we define an edge labeling f : E(P(n.(Cr�P2))) → Zk − {0} as follows:

f(v
j
i u

j
i) = k − 2a, for i = 1, 2, . . . , r, j = 1, 2, . . . , n − 1,

f(v
j
i v

j
i+1) = a, for i = 1, 2, . . . , r, j = 1, 2, . . . , n − 1,

f(u1i u
1
i+1) =

{

k − a, for i = 1, 3, . . . , r,

3a, for i = 2, 4, . . . , r − 1,

f(u
j
iu

j
i+1) = a, for i = 1, 2, . . . , r, j = 2, 3, . . . , n − 1,

f(vni v
n
i+1) =

{

k − a, for n is odd,

a, for n is even,

f(vni u
n
i ) =

{

2a, for n is odd,

k − 2a, for n is even,

f(uni u
n
i+1) =



















a, for i = 1, 3, . . . , r and n is odd,

k − 3a, for i = 2, 4, . . . , r − 1 and n is odd,

k − a, for i = 1, 3, . . . , r and n is even,

3a, for i = 2, 4, . . . , r − 1 and n is even,

f(u
j
1u

j+1
1 ) =

{

4a, for j = 1, 3, . . . , j ≤ n − 1,

k − 4a, for j = 2, 4, . . . , j ≤ n − 1.

Then the induced vertex labeling f+ : V (P(n.(Cr�P2))) → Zk is f
+(v) ≡ 0 ≡ k for all v ∈

V (P(n.(Cr�P2))). Hence f
+ is constant and is equal to 0 ≡ k.

An example of a Z9-magic labeling of P(3.(C7�P2)) is shown in Figure 8.

1

2

3

4

8

7

2
2

2

2

2

2

2

5

5

5

5

5

5

5
7

77

6

6
7

2
2

2

2

2

2

2

5

5

5

5

5

5

5

b b b

2

2

2

2

2

2

2

22

7

7

7
7

7

7

4

4

44

4

4

3

3

2

b

b

bb

b

b

b

b

b

bb

b b

b

b

bb

b

b

b

b

b b

b

b

b

b
b

b

bb

b

b

b b

b

b
b

6

b

Figure 8: A Z9-magic labeling of P(3.(C7�P2)
v).



32 YP. Jeyanthi, K. Jeya Daisy and Andrea Semaničová-Feňovč́ıková CUBO
21, 2 (2019)

Theorem 2.9. Let r ≥ 5 and n ≥ 2 be positive integers. The path union of a total graph of a path

P(n.T (Pr)
v), where v ∈ V (T (Pr)) is a vertex of degree two, is Zk-magic for k ≥ 3.

Proof. Let the vertex set and the edge set of P(n.T (Pr)
v) be V (P(n.T (Pr)

v)) = {u
j
i
: 1 ≤ i ≤

r, 1 ≤ j ≤ n} ∪ {v
j
i : 1 ≤ i ≤ r − 1, 1 ≤ j ≤ n} and E(P(n.T (Pr)

v)) = {u
j
iu

j
i+1 : 1 ≤ i ≤ r − 1, 1 ≤

j ≤ n} ∪ {v
j
i v

j
i+1 : 1 ≤ i ≤ r − 2, 1 ≤ j ≤ n} ∪ {u

j
i+1v

j
i : 1 ≤ i ≤ r − 1, 1 ≤ j ≤ n} ∪ {u

j
iv

j
i : 1 ≤ i ≤

r − 1, 1 ≤ j ≤ n} ∪ {u
j
1u

j+1
1 : 1 ≤ j ≤ n − 1}.

We consider the following two cases according to the parity of r.

Case (i): when r is odd.

Let a, k be positive integers, k > 2a. Thus k ≥ 3.

Define an edge labeling f : E(P(n.T (Pr)
v)) → Zk − {0} as follows:

f(u1i u
1
i+1) =

{

a, for i = 1, 3, . . . , r,

2a, for i = 2, 4, . . . , r − 3,

f(u1r−1u
1
r) = f(v

1
1v

1
2) = a,

f(v1i v
1
i+1) =

{

2a, for i = 3, 5, . . . , r,

a, for i = 2, 4, . . . , r − 1,

f(u11v
1
1) = a,

f(u12v
1
2) = k − a,

f(u1i v
1
i ) = k − 2a, for i = 3, 4, . . . , r − 2,

f(u1r−1v
1
r−1) = k − a,

f(v11u
1
2) = k − 2a,

f(v1i u
1
i+1) = k − a, for i = 2, 3, . . . , r − 1,

f(u
j
1v

j
1) = f(u

j
2v

j
1) = a, for j = 2, 3, . . . , n − 1,

f(u
j
1u

j
2) = f(u

j
r−1u

j
r) = k − a, for j = 2, 3, . . . , n − 1,

f(u
j
iu

j
i+1) = k − 2a, for i = 2, 3, . . . , r − 2, j = 2, 3, . . . , n − 1,

f(v
j
i
v
j
i+1) = k − 2a, for i = 1, 2, . . . , r − 2, j = 2, 3, . . . , n − 1,

f(u
j
iv

j
i ) = f(u

j
i+1v

j
i ) = 2a, for i = 2, 3, . . . , r − 2, j = 2, 3, . . . , n − 1,

f(ujrv
j
r−1) = f(u

j
r−1v

j
r−1) = a, for j = 2, 3, . . . , n − 1,



CUBO
21, 2 (2019)

Zk-Magic Labeling of Path Union of Graphs 33

f(unr−1u
n
r ) =

{

k − a, for n is odd,

a, for n is even,

f(uni u
n
i+1) =



















k − a, for i = 1, 3, . . . , r and n is odd,

k − 2a, for i = 2, 4, . . . , r − 3 and n is odd,

a, for i = 1, 3, . . . , r and n is even,

2a, for i = 2, 4, . . . , r − 3 and n is odd,

f(vn1 v
n
2 ) =

{

k − a, for n is odd,

a, for n is even,

f(vni v
n
i+1) =



















k − 2a, for i = 3, 5, . . . , r and n is odd,

k − a, for i = 2, 4, . . . , r − 1 and n is odd,

2a, for i = 3, 5, . . . , r and n is even,

a, for i = 2, 4, . . . , r − 1 and n is even,

f(un1 v
n
1 ) =

{

k − a, for n is odd,

a, for n is even,

f(un2 v
n
2 ) =

{

a, for n is odd,

k − a, for n is even,

f(uni v
n
i ) =

{

2a, for i = 3, 4, . . . , r − 2 and n is odd,

k − 2a, for i = 3, 4, . . . , r − 2 and n is even,

f(unr−1v
n
r−1) =

{

a, for n is odd,

k − a, for n is even,

f(vn1 u
n
2 ) =

{

2a, for n is odd,

k − 2a, for n is even,

f(vni u
n
i+1) =

{

a, for i = 2, 3, . . . , r − 1 and n is odd,

k − a, for i = 2, 3, . . . , r − 1 and n is even,

f(u
j
1u

j+1
1 ) =

{

k − 2a, for j = 1, 3, . . . and j ≤ n − 1,

2a, for j = 2, 4, . . . and j ≤ n − 1.

Then the induced vertex labeling f+ : V (P(n.T (Pr)
v)) → Zk is f

+(u) ≡ 0 (mod k) for all u ∈

V (P(n.T (Pr)
v)).



34 YP. Jeyanthi, K. Jeya Daisy and Andrea Semaničová-Feňovč́ıková CUBO
21, 2 (2019)

Case (ii): when r is even.

Let a, k be positive integers, k > 2a. Thus k ≥ 3.

Define an edge labeling f : E(P(n.T (Pr)
v)) → Zk − {0} as follows:

f(u1i u
1
i+1) = f(v

1
i v

1
i+1) =

{

k − a, for i = 1, 3, . . . , r − 1,

k − 2a, for i = 2, 4, . . . , r,

f(v11u
1
1) = k − a,

f(v1i u
1
i ) = a, for i = 2, 3, . . . , r − 1,

f(v1i u
1
i+1) = 2a, for i = 1, 2, . . . , r − 2,

f(v1r−1u
1
r) = a,

f(u
j
1v

j
1) = f(u

j
2v

j
1) = a, for j = 2, 3, . . . , n − 1,

f(u
j
1u

j
2) = f(u

j
r−1u

j
r) = k − a, for j = 2, 3, . . . , n − 1,

f(u
j
i u

j
i+1) = k − 2a, for i = 2, 3, . . . , r − 2, j = 2, 3, . . . , n − 1,

f(v
j
i v

j
i+1) = k − 2a, for i = 1, 2, . . . , r − 2, j = 2, 3, . . . , n − 1,

f(u
j
i v

j
i ) = f(u

j
i+1v

j
i ) = 2a, for i = 2, 3, . . . , r − 2, j = 2, 3, . . . , n − 1,

f(ujrv
j
r−1) = f(u

j
r−1v

j
r−1) = a, for j = 2, 3, . . . , n − 1,

f(uni u
n
i+1) = f(v

n
i v

n
i+1) =



















a, for i = 1, 3, . . . , r − 1 and n is odd,

2a, for i = 2, 4, . . . , r and n is odd,

k − a, for i = 1, 3, . . . , r − 1 and n is even,

k − 2a, for i = 2, 4, . . . , r and n is even,

f(un1 v
n
1 ) =

{

a, for n is odd,

k − a, for n is even,

f(uni v
n
i ) =

{

k − a, for i = 2, 3, . . . , r − 1 and n is odd,

a, for i = 2, 3, . . . , r − 1 and n is even,

f(vni u
n
i+1) =

{

k − 2a, for i = 1, 2, . . . , r − 2 and n is odd,

2a, for i = 1, 2, . . . , r − 2 and n is even,

f(vnr−1u
n
r ) =

{

k − a, for n is odd,

a, for n is even,

f(u
j
1u

j+1
1 ) =

{

2a, for j = 1, 3, . . . and j ≤ n − 1,

k − 2a, for j = 2, 4, . . . and j ≤ n − 1.

Then the induced vertex labeling f+ : V (P(n.T (Pr)
v)) → Zk is f

+(u) ≡ 0 (mod k) for all u ∈

V (P(n.T (Pr)
v)). Hence P(n.T (Pr)

v) is a Zk-magic graph.



CUBO
21, 2 (2019)

Zk-Magic Labeling of Path Union of Graphs 35

An example of a Z5-magic labeling of P(5.T (P6)
v) is shown in Figure 9.

b

b

b

b

b

b

b

b

b

b

b

b

b

b

b

b

b

b

b

b

b

b

b

b

b

b

b

b

b

b

b

b

b

b

b

b

b

b

b

b

b

b

b

b

b

b

b

b

b

b

b

b

b

b

b

b b b b b

1

2

3

4

3

3

3

3

4

4

4

4

1

1

1

2

2

2

2

1

11

1

4

4

3

3

3

3

4

4

3

3

2

2

2

2

2

2

1

2

2

2

2

2

2 2

4
3

3

3

3

3

3

3

3

3

1

1

1

1

1

1

1

1

4

4

3

3

3

3

33

2

2

2

2

2

2

2

2

2

2

4

4

4

4

4

11

1

1

1

1

3

3

3

33

Figure 9: A Z5-magic labeling of P(5.T (P6)
v).

Theorem 2.10. Let r ≥ 3 and n ≥ 2 be integers. Let v is a vertex of degree 2 in LCr. The path

union of a lotus inside a circle graph P(n.LCvr ), is Zk-magic for k ≥ r.

Proof. Let the vertex set and the edge set of P(n.LCvr ) be V (P(n.LC
v
r )) = {wj, v

j
i , u

j
i : 1 ≤ i ≤

r, 1 ≤ j ≤ n} and E(P(n.LCvr )) = {wjv
j
i : 1 ≤ i ≤ r, 1 ≤ j ≤ n} ∪ {v

j
i u

j
i : 1 ≤ i ≤ r, 1 ≤ j ≤

n} ∪ {v
j
i u

j
i+1 : 1 ≤ i ≤ r, 1 ≤ j ≤ n} ∪ {u

j
iu

j
i+1 : 1 ≤ i ≤ r, 1 ≤ j ≤ n} ∪ {u

j
1u

j+1
1 : 1 ≤ j ≤ n − 1},

where the index i is taken over modulo r.

We consider the following two cases according to the parity of r.

Case (i): when r is odd.

Let a, k be positive integers, k > (r − 1)a. Thus k ≥ r.



36 YP. Jeyanthi, K. Jeya Daisy and Andrea Semaničová-Feňovč́ıková CUBO
21, 2 (2019)

Define an edge labeling f : E(P(n.LCvr )) → Zk − {0} in the following way.

f(wjv
j
1) = k − (r − 1)a, for j = 1, 2, . . . , n − 1,

f(wjv
j
i
) = a, for i = 2, 3, . . . , r, j = 1, 2, . . . , n − 1,

f(v
j
1u

j
1) = (r − 2)a, for j = 1, 2, . . . , n − 1,

f(v
j
i u

j
i ) = k − 2a, for i = 2, 3, . . . , r, j = 1, 2, . . . , n − 1,

f(v
j
i u

j
i+1) = a, for i = 1, 2, . . . , r, j = 1, 2, . . . , n − 1,

f(u1i u
1
i+1) =

{

k − a, for i = 1, 3, . . . , r,

2a, for i = 2, 4, . . . , r − 1,

f(u
j
iu

j
i+1) =

{

k −
(r−1)a

2
, for i = 1, 3, . . . , r, j = 2, 3, . . . , n − 1,

(r+1)a
2

, for i = 2, 4, . . . , r − 1, j = 2, 3, . . . , n − 1,

f(u
j
1u

j+1
1 ) =

{

k − (r − 3)a, for j = 1, 3, . . . , j ≤ n − 1,

(r − 3)a, for j = 2, 4, . . . , j ≤ n − 1,

f(wnv
n
1 ) =

{

(r − 1)a, for n is odd,

k − (r − 1)a, for n is even,

f(wnv
n
i ) =

{

k − a, for i = 2, 3, . . . , r and n is odd,

a, for i = 2, 3, . . . , r and n is even,

f(vn1 u
n
1 ) =

{

k − (r − 2)a, for n is odd,

(r − 2)a, for n is even,

f(vni u
n
i ) =

{

2a, for i = 2, 3, . . . , r and n is odd,

k − 2a, for i = 2, 3, . . . , r and n is even,

f(vni u
n
i+1) =

{

k − a, for i = 1, 2, . . . , r and n is odd,

a, for i = 1, 2, . . . , r and n is even,

f(uni u
n
i+1) =



















a, for i = 1, 3, . . . , r and n is odd,

k − 2a, for i = 2, 4, . . . , r − 1 and n is odd,

k − a, for i = 1, 3, . . . , r and n is even,

2a, for i = 2, 4, . . . , r − 1 and n is even.

Then the induced vertex labeling f+ : V (P(n.LCvr )) → Zk is f
+(u) ≡ 0 (mod k) for all u ∈

V (P(n.LCvr )).

Case (ii): when r is even.

Let a, k be positive integers, k > (r − 1)a. Thus k ≥ r.



CUBO
21, 2 (2019)

Zk-Magic Labeling of Path Union of Graphs 37

Define an edge labeling f : E(P(n.LCr)) → Zk − {0} as follows:

f(w1v
1
1) = k − (r − 1)a,

f(w1v
1
i ) = a, for i = 2, 3, . . . , r,

f(v11u
1
1) = (r − 2)a,

f(v1i u
1
i ) = k − 2, for i = 2, 3, . . . , r,

f(v1i u
1
i+1) = a, for i = 1, 2, . . . , r,

f(u1i u
1
i+1) =

{

k − a, for i = 1, 3, . . . , r − 1,

2a, for i = 2, 4, . . . , r,

f(wjv
j
i
) =

{

a, for i = 1, 3, . . . , r − 1, j = 2, 3, . . . , n − 1,

k − a, for i = 2, 4, . . . , r, j = 2, 3, . . . , n − 1,

f(v
j
i u

j
i) =

{

k − 2a, for i = 1, 3, . . . , r − 1, j = 2, 3, . . . , n − 1,

k − a, for i = 2, 4, . . . , r, j = 2, 3, . . . , n − 1,

f(v
j
i u

j
i+1) =

{

a, for i = 1, 3, . . . , r − 1, j = 1, 2, . . . , n − 1,

2a, for i = 2, 4, . . . , r, j = 1, 2, . . . , n − 1,

f(u
j
i u

j
i+1) =

{

k − a, for i = 1, 3, . . . , r − 1, j = 2, 3, . . . , n − 1,

a, for i = 2, 4, . . . , r, j = 2, 3, . . . , n − 1,

f(wnv
n
1 ) =

{

(r − 1)a, for n is odd,

k − (r − 1)a, for n is even,

f(wnv
n
i ) =

{

k − a, for i = 2, 3, . . . , r and n is odd,

a, for i = 2, 3, . . . , r and n is even,

f(vn1 u
n
1 ) =

{

k − (r − 2)a, for n is odd,

(r − 2)a, for n is even,

f(vni u
n
i ) =

{

2a, for i = 2, 3, . . . , r and n is odd,

k − 2a, for i = 2, 3, . . . , r and n is even,

f(vni u
n
i+1) =

{

k − a, for i = 1, 2, . . . , r and n is odd,

a, for i = 1, 2, . . . , r and n is even,

f(uni u
n
i+1) =



















a, for i = 1, 3, . . . , r − 1 and n is odd,

k − 2a, for i = 2, 4, . . . , r and n is odd,

k − a, for i = 1, 3, . . . , r − 1 and n is even,

2a, for i = 2, 4, . . . , r and n is even,

f(u
j
1u

j+1
1 ) =

{

k − ra, for j = 1, 3, . . . , j ≤ n − 1,

ra, for j = 2, 4, . . . , j ≤ n − 1.

Then the induced vertex labeling f+ : V (P(n.LCvr )) → Zk is f
+(u) ≡ 0 (mod k) for all u ∈



38 YP. Jeyanthi, K. Jeya Daisy and Andrea Semaničová-Feňovč́ıková CUBO
21, 2 (2019)

V (P(n.LCvr )). Hence f
+ is constant and is equal to ≡ 0 (mod k).

An example of a Z10-magic labeling of P(3.LC
v
6 ) is shown in Figure 10.

b

b

b

bb

b

b

b

b

b

b

b

b

b

b

b

bb

b

b

b

b

b

b

b

b

b

b

b

bb

b

b

b

b

b

b

b

b

b b b

1

2

4

5

6

8

9

1
1

1

1

1
1

1

1

1

8

8

8

8

1

1

1

9

9
9

2

2 4

1

1

1

9

9

2
8

9

2

2

8

8
9

1

9

9

9
9

9 5

6
9

9

9

9

9

9

2

2
2

2

2

1

8

1

1

8

8
9

9

9

1

1

1

9

Figure 10: A Z10-magic labeling of P(3.LC
v
6 ).

In the last theorem we deal with the path union of an r-pan graph P(n.(r-pan)v), where v is

a vertex of degree two in an r-pan graph.

Theorem 2.11. Let r ≥ 3, n ≥ 2 be integers. The path union of an r-pan graph P(n.(r-pan)v),

where v is a vertex of degree two in an r-pan graph, is Zk-magic for k ≥ 5 when r is odd.

Proof. Let v be a vertex of degree two in an r-pan graph. Let the vertex set and the edge set of

P(n.(r-pan)v) be V (P(n.(r-pan)v)) = {wj, v
j
i : 1 ≤ i ≤ r, 1 ≤ j ≤ n} and E(P(n.(r-pan)

v)) =

{v
j
i v

j
i+1 : 1 ≤ i ≤ r, 1 ≤ j ≤ n} ∪ {v

j
1wj : 1 ≤ j ≤ n} ∪ {w

j
1w

j+1
1 : 1 ≤ j ≤ n − 1}, where the index

i is taken over modulo r.

Let a, k be positive integers, k > 2a. Thus k ≥ 5.

For r odd we define an edge labeling f : E(P(n.(r-pan)v)) → Zk − {0} as follows:

f(v1i v
1
i+1) = f(v

n
i v

n
i+1) =

{

k − a, for i = 1, 3, . . . , r,

a, for i = 2, 4, . . . , r − 1,

f(v
j
i v

j
i+1) =

{

k − 2a, for i = 1, 3, . . . , r, j = 2, 3, . . . , n − 1,

2a, for i = 2, 4, . . . , r − 1, j = 2, 3, . . . , n − 1,

f(v11w1) = f(v
n
1 wn) = 2a,

f(v
j
1wj) = 4a, for j = 2, 3, . . . , n − 1,

f(w
j
1w

j+1
1 ) = k − 2a, for j = 1, 2, . . . , n − 1.

Then the induced vertex labeling f+ : V (P(n.(r-pan)v)) → Zk is f
+(u) ≡ 0 (mod k) for all

u ∈ V (P(n.(r-pan)v)). This means that P(n.(r-pan)v) is a Zk-magic graph.

An example of a Z9-magic labeling of P(4.(5-pan)
v) is illustrated in Figure 11.



CUBO
21, 2 (2019)

Zk-Magic Labeling of Path Union of Graphs 39

b

b

b
b

b

b

2

7

7 7

2

5

b

b

b
b

b

b

8

b

b

b
b

b

b

8

b

b

b
b

b

b

2

7

7 7

2

b bbb
5

5

5 5

4

4
4

5

5

55

4

4
4

Figure 11: A Z9-magic labeling of P(4.(5-pan)
v).

Acknowledgment

This work was supported by the Slovak Research and Development Agency under the contract No.

APVV-15-0116 and by VEGA 1/0233/18.



40 YP. Jeyanthi, K. Jeya Daisy and Andrea Semaničová-Feňovč́ıková CUBO
21, 2 (2019)

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	Introduction
	Zk-Magic Labeling of Path Union of Graphs