Edelweiss Applied Science and Technology ISSN: 2576-8484 Vol. 8, No. 6, 4408-4414 2024 Publisher: Learning Gate DOI: 10.55214/25768484.v8i6.2965 Β© 2024 by the authors; licensee Learning Gate Β© 2024 by the authors; licensee Learning Gate * Correspondence: amarachandoul@yahoo.fr Solutions of the equation π’™πŸ βˆ’ (π’‘πŸπ’’πŸ Β± 𝐚𝐩)π’šπŸ = π’Œπ’• Amara Chandoul1*, Alanod Sibih2 1Department of Computer Science 𝖠Multimedia, Higher Institute of Informatics 𝖠Multimedia of Sfax, Tunis Road, Km 10, Al βˆ’Ons, B. P. 242, 3021, Tunisia; amarachandoul@yahoo.fr (A.C.) 2Department of Mathematics, Jamoum University College, Umm Al βˆ’Qura University, Holly Makkah 21955, Saudi Arabia; amsibih@uqu.edu.sa (A.S.). Abstract: In this note, the Diophantine equation π‘₯2 βˆ’ (𝑝2π‘ž2 Β± ap)𝑦2 = π‘˜π‘‘ has been solved, and its positive integer solutions have been stated in terms of generalized Fibonacci, generalized Lucas, generalized Pell, and generalized Pell-Lucas sequences. We have discovered units for 𝑍[𝐷] in terms of the above sequences of numbers. Keywords: Diophantine equations, Generalized Fibonacci numbers, Generalized Lucas numbers, Generalized Pell numbers, Generalized Pell–Lucas numbers, Pell equations. 1. Introduction Since ancient times, numerous mathematicians have studied number sequences. Particular attention has been paid to recurrent sequences like the Fibonacci, Lucas, Pell, or Pell-Lucas sequences, which are described below: Fibonacci number sequence 𝐹𝑛+2 = 𝐹𝑛+1 + 𝐹𝑛 for 𝑛 β‰₯ 0 with 𝐹0 = 0 and 𝐹1 = 1. Lucas number sequence 𝐿𝑛+2 = 𝐿𝑛+1 + 𝐿𝑛 for 𝑛 β‰₯ 0 with 𝐿0 = 2 and 𝐿1 = 1. Pell number sequence Φ𝑛+2 = 2Φ𝑛+1 + Φ𝑛 for 𝑛 β‰₯ 0 with Ξ¦0 = 0 and Ξ¦1 = 1. Pell-Lucas number sequence Ψ𝑛+2 = 2Ψ𝑛+1 + Ψ𝑛 for 𝑛 β‰₯ 0 with Ξ¨0 = 2 and Ξ¨1 = 2. In recent years, these sequences of numbers have significant applications in the fields including statistics, music, coding theory, cryptography and communication systems. [2], [3], [4]. As seen in [11,12,13], number sequences are generalized in several ways. One can see some generalizations of Pell and Pell–Lucas numbers. In this paper we will pay attention to the following generalization: Let 𝑠 and 𝑑 be two non-zero integers satisfying 𝑠2 + 4𝑑 > 0, The generalized Fibonacci and generalized Lucas sequences are, respectively, defined as: 𝐹𝑛+2(𝑠, 𝑑) = 𝑠𝐹𝑛+1(𝑠, 𝑑) + 𝑑𝐹𝑛(𝑠, 𝑑) for 𝑛 β‰₯ 0 with 𝐹0(𝑠, 𝑑) = 0, 𝐹1(𝑠, 𝑑) = 1, and 𝐿𝑛+2(𝑠, 𝑑) = 𝑠𝐿𝑛+1(𝑠, 𝑑) + 𝑑𝐿𝑛(𝑠, 𝑑) for 𝑛 β‰₯ 0 with 𝐿0(𝑠, 𝑑) = 2, 𝐿1(𝑠, 𝑑) = 1, Binet’s formulae for these sequences are: 4409 Edelweiss Applied Science and Technology ISSN: 2576-8484 Vol. 8, No. 6: 4408-4414, 2024 DOI: 10.55214/25768484.v8i6.2965 Β© 2024 by the authors; licensee Learning Gate 𝐹𝑛(𝑠, 𝑑) = π›Όπ‘›βˆ’ 𝛽𝑛 π›Όβˆ’π›½ , 𝐿𝑛(𝑠, 𝑑) = 𝛼 𝑛 + 𝛽𝑛, where 𝛼 and 𝛽 are the roots of equation π‘₯2 βˆ’ 𝑠π‘₯ βˆ’ 𝑑 = 0. 𝛼 and 𝛽 verify 𝛼 + 𝛽 = 𝑠, 𝛼 βˆ’ 𝛽 = 2βˆšπ‘ 2 + 4𝑑, 𝛼𝛽 = βˆ’π‘‘. For further details of these sequences, see [5], [6], [7],[17], [18], [19], [20],[21]. Let, now, π‘˜ and β„Ž be two non-zero integers satisfying π‘˜2 + β„Ž > 0, The generalized Pell and generalized Pell-Lucas sequences are, respectively, defined as: Φ𝑛+2(π‘˜, β„Ž) = 2π‘˜Ξ¦π‘›+1(π‘˜, β„Ž) + β„ŽΞ¦π‘›(π‘˜, β„Ž) for 𝑛 β‰₯ 0 with Ξ¦0(π‘˜, β„Ž) = 0 and Ξ¦1(π‘˜, β„Ž) = 1, and Ψ𝑛+2(π‘˜, β„Ž) = 2π‘˜Ξ¨π‘›+1(π‘˜, β„Ž) + β„ŽΞ¨π‘›(π‘˜, β„Ž) for 𝑛 β‰₯ 0 with Ξ¨0(π‘˜, β„Ž) = 2 and Ξ¨1(π‘˜, β„Ž) = 2π‘˜ Binet’s formulae for these sequences are: Φ𝑛(π‘˜, β„Ž) = 2π‘˜ π›Όπ‘›βˆ’ 𝛽𝑛 π›Όβˆ’π›½ , Ψ𝑛(π‘˜, β„Ž) = 𝛼 𝑛 + 𝛽𝑛, where 𝛼 and 𝛽 are the roots of equation π‘₯2 βˆ’ 2π‘˜π‘₯ βˆ’ β„Ž = 0. 𝛼 and 𝛽 verify 𝛼 + 𝛽 = 2π‘˜, 𝛼 βˆ’ 𝛽 = 2βˆšπ‘˜2 + β„Ž, 𝛼𝛽 = βˆ’β„Ž. In the plethora of integer sequences, the Fibonacci and Lucas sequences stand out as the two brightest. They have captivated both amateur and expert mathematicians for ages, and they never cease to enchant us with their beauty, myriad practical uses, and omnipresent propensity to appear in completely unexpected and unrelated contexts. They continue to be a fertile ground for creative amateurs and mathematicians alike. In literature, Fibonacci and Lucas numbers are used to resolve many Diophantine equations. The quadratic Diophantine equation of the form π‘₯2 βˆ’ 𝐷𝑦2 = 𝑁, where 𝐷 is square free, generally known as Pell’s equation. In this case, if 𝐷 is square free, the continued fraction expansion of 𝐷 is periodic and it is given by 𝐷 = π‘Ž0; π‘Ž1 , π‘Ž2 ,β‹― π‘Žπ‘›βˆ’1, π‘Žπ‘›Μ…Μ… Μ…Μ… Μ…Μ… Μ…Μ… Μ…Μ… Μ…Μ… Μ…Μ… Μ…Μ… Μ…Μ… Μ…Μ… Μ…Μ… Μ…, where π‘Žπ‘› = 2π‘Ž0 and 𝑛 is the length of period. As it is known, we denote by 𝑝1 π‘ž1 = [π‘Ž0; π‘Ž1 , π‘Ž2 ,β‹― π‘Žπ‘™] the π‘™π‘‘β„Ž convergent of 𝐷, for 𝑙 β‰₯ 0. In (5), we have obtained some formulas for the integer solutions of the Pell equation π‘₯2 βˆ’ 𝑦2 = Β±π‘˜2 for all π‘˜ β‰₯ 1. In [9], Bala and Mishra, considered the solutions of two Diophantine equations π‘₯2 βˆ’ (𝑝2π‘ž2 Β± 3p)𝑦2 = π‘˜π‘‘ and π‘₯2 βˆ’ (𝑝2π‘ž2 Β± 5p)𝑦2 = π‘˜π‘‘. They generalized a previous result of Guney [10], who found all positive integer solutions of the equations π‘₯2 βˆ’ (π‘Ž2𝑏2 + 2𝑏)𝑦2 = 𝑁 when 𝑁 ∈ {Β±1,Β±4} in terms of generalized Fibonacci and Lucas sequences. In this paper, we generalize the results of Bala and Mishra [9], by solving π‘₯2 Β± (𝑝2π‘ž2 βˆ’ π‘Žπ‘)𝑦2 = π‘˜π‘‘ Then we express its positive integer solutions in the current study. Using generalized Lucas, generalized Pell, and generalized Pell-Lucas sequences. To do, we need the following theorems (1,2,3,2.1): Theorem 1, There is no positive integer solution to the equation π‘₯2 βˆ’ 𝐷𝑦2 = βˆ’1 if the length of the period of √𝐷 's continued fraction expansion is even, while the fundamental solution of equation π‘₯2 βˆ’ 𝐷𝑦2 = 1 is π‘π‘›βˆ’1 π‘žπ‘›βˆ’1 . 4410 Edelweiss Applied Science and Technology ISSN: 2576-8484 Vol. 8, No. 6: 4408-4414, 2024 DOI: 10.55214/25768484.v8i6.2965 Β© 2024 by the authors; licensee Learning Gate Theorem 2, There are infinitely many solutions to the Pell equation π‘₯2 βˆ’ 𝐷𝑦2 = 1 if 𝐷 is a natural number that is not a perfect square. All positive solutions can be obtained by the formula π‘₯𝑛 + π‘¦π‘›βˆšπ· = (π‘₯1 + 𝑦1√𝐷) 𝑛, for all 𝑛 > 1, where (π‘₯1, 𝑦1) is fundamental solution of equation π‘₯2 βˆ’ 𝐷𝑦2 = 1. Theorem 3, Let 𝑁 be a positive integer and (𝑒1, 𝑣1) be the fundamental solution of equation π‘₯2 βˆ’ 𝐷𝑦2 = 𝑁. Then all positive solutions of π‘₯2 βˆ’ 𝐷𝑦2 = 𝑁 can be obtained by the formula π‘₯𝑛 + π‘¦π‘›βˆšπ· = (𝑒1 + 𝑣1√𝐷)(π‘₯1 + 𝑦1√𝐷) 𝑛, for all 𝑛 > 1, where (π‘₯1, 𝑦1) is fundamental solution of equation π‘₯2 βˆ’ 𝐷𝑦2 = 1. We are now ready to present our main results. 2. Main Results 2.1. Theorem Let 𝐷 = 𝑝2π‘ž2 βˆ’ π‘Žπ‘, with π‘ž > π‘Ž being a multiple of π‘Ž and 𝑝, π‘ž being positive integers chosen in such a way that 𝐷 is not a perfect square, then 1. √𝐷 = βˆšπ‘2π‘ž2 βˆ’ π‘Žπ‘ = [π‘π‘ž βˆ’ 1; 1, 2(π‘žβˆ’π‘Ž) π‘Ž , 1, 29π‘π‘ž βˆ’ 1) Μ…Μ… Μ…Μ… Μ…Μ… Μ…Μ… Μ…Μ… Μ…Μ… Μ…Μ… Μ…Μ… Μ…Μ… Μ…Μ… Μ…Μ… Μ…Μ… Μ…Μ… Μ…Μ… ]. 2. The fundamental solution of the Pell equation π‘₯2 βˆ’ 𝐷𝑦2 = 1 is (π‘₯1, 𝑦1) = ( 2π‘π‘ž2βˆ’π‘Ž π‘Ž , 2π‘ž π‘Ž ). 3. All positive integer solution (π‘₯𝑛, 𝑦𝑛) of the Pell equation π‘₯2 βˆ’ 𝐷𝑦2 = 1 are provided by π‘₯𝑛 = 𝛼𝑛+𝛽2 2 = 1 2 𝑙𝑛(𝑠, 𝑑) = 1 2 𝑙𝑛 (2 2π‘π‘ž2βˆ’π‘Ž π‘Ž , βˆ’1), and 𝑦𝑛 = 𝛼𝑛+𝛽2 2√𝐷 = 2π‘ž π‘Ž 𝐹𝑛(𝑠, 𝑑) = 2π‘ž π‘Ž 𝐹𝑛 (2 2π‘π‘ž2βˆ’π‘Ž π‘Ž , βˆ’1) = π‘ž 2π‘π‘ž2βˆ’π‘Ž Φ𝑛 (2 2π‘π‘ž2βˆ’π‘Ž π‘Ž , βˆ’1) , for all 𝑛 β‰₯ 1. 1. The Fundamental solution of Pell equation π‘₯2 βˆ’ 𝐷𝑦2 = π‘˜π‘‘ is (π‘₯1, 𝑦1) = ( 2π‘π‘ž2 βˆ’ π‘Ž π‘Ž π‘˜ 𝑑 2, 2π‘ž π‘Ž π‘˜ 𝑑 2). 2. All positive solutions of Pell equation π‘₯2 βˆ’ 𝐷𝑦2 = π‘˜π‘‘is given by π‘₯𝑛+1 = 2π‘π‘ž2βˆ’π‘Ž π‘Ž π‘˜ 𝑑 2π‘₯𝑛 + 2π‘ž 𝑝2π‘ž2βˆ’π‘Žπ‘ π‘Ž π‘˜ 𝑑 2𝑦𝑛 and 𝑦𝑛+1 = 2π‘ž π‘Ž π‘˜ 𝑑 2π‘₯𝑛 + 2π‘π‘ž2βˆ’π‘Ž π‘Ž π‘˜ 𝑑 2𝑦𝑛 for all 𝑛 β‰₯ 1 Proof: 1. √D = √p2q2 βˆ’ ap = (pq βˆ’ 1) + √p2q2 βˆ’ ap βˆ’ (pq βˆ’ 1) 4411 Edelweiss Applied Science and Technology ISSN: 2576-8484 Vol. 8, No. 6: 4408-4414, 2024 DOI: 10.55214/25768484.v8i6.2965 Β© 2024 by the authors; licensee Learning Gate = (pq βˆ’ 1) + 1 √p2q2βˆ’ap+(pqβˆ’1) 2pqβˆ’apβˆ’1 = (pq βˆ’ 1) + 1 1 + √p2q2βˆ’apβˆ’(pqβˆ’ap) 2pqβˆ’apβˆ’1 = (pq βˆ’ 1) + 1 1 + 1 √p2q2βˆ’ap+(pqβˆ’ap) ap = (pq βˆ’ 1) + 1 1 + 1 2(qβˆ’a) a + √p2q2βˆ’apβˆ’(pqβˆ’ap) ap = (pq βˆ’ 1) + 1 1 + 1 2(qβˆ’a) a + 1 1+ 1 2(pqβˆ’1)+√p2q2βˆ’apβˆ’(pqβˆ’1) = [pq βˆ’ 1; 1, 2(q βˆ’ a) a , 1,2(pq βˆ’ 1) Μ…Μ… Μ…Μ… Μ…Μ… Μ…Μ… Μ…Μ… Μ…Μ… Μ…Μ… Μ…Μ… Μ…Μ… Μ…Μ… Μ…Μ… Μ…Μ… Μ…Μ… Μ…Μ… Μ…Μ… ] 2. The period length of √𝐷 's continued fraction expansion is 4, making it even. Then, according to Theorem 1.1, the fundamental solution of equation π‘₯2 βˆ’ 𝐷𝑦2 = 1 is given by 𝑝3 π‘Ž π‘ž3 π‘Ž . Let 𝑝3 π‘ž3 = [π‘π‘ž βˆ’ 1; 1, 2(π‘žβˆ’π‘Ž) π‘Ž , 1] = (π‘π‘ž βˆ’ 1) + 1 1+ 2(π‘žβˆ’π‘Ž) π‘Ž +1 = 2π‘π‘ž2βˆ’π‘Ž 2π‘ž . Then, (π‘₯1, 𝑦1) = ( 2π‘π‘ž2βˆ’π‘Ž π‘Ž , 2π‘ž π‘Ž ). 3. According to Theorem 1.1, all of the positive integral solutions to the equation π‘₯2 βˆ’ 𝐷𝑦2 = 1 is provided by π‘₯𝑛 + π‘¦π‘›βˆšπ· = ( 2π‘π‘ž2βˆ’π‘Ž π‘Ž + 2π‘ž π‘Ž √𝐷) 𝑛 , and π‘₯𝑛 βˆ’ π‘¦π‘›βˆšπ· = ( 2π‘π‘ž2βˆ’π‘Ž π‘Ž βˆ’ 2π‘ž π‘Ž √𝐷) 𝑛 Set 𝛼 = 2π‘π‘ž2βˆ’π‘Ž π‘Ž + 2π‘ž π‘Ž √𝐷 and 𝛽 = 2π‘π‘ž2βˆ’π‘Ž π‘Ž βˆ’ 2π‘ž π‘Ž √𝐷, then 𝛼 + 𝛽 = 2( 2π‘π‘ž2βˆ’π‘Ž π‘Ž ) and 𝑑 = βˆ’π›Όπ›½ = βˆ’1. Thus, for all 𝑛 β‰₯ 1. π‘₯𝑛 = 𝛼𝑛+𝛽𝑛 2 = 1 2 𝐿𝑛(𝑠, 𝑑) = 1 2 𝐿𝑛 (2 2π‘π‘ž2βˆ’π‘Ž π‘Ž , βˆ’1) = 1 2 Ψ𝑛 ( 2π‘π‘ž2βˆ’π‘Ž π‘Ž , βˆ’1), 4412 Edelweiss Applied Science and Technology ISSN: 2576-8484 Vol. 8, No. 6: 4408-4414, 2024 DOI: 10.55214/25768484.v8i6.2965 Β© 2024 by the authors; licensee Learning Gate and 𝑦𝑛 = π›Όπ‘›βˆ’π›½π‘› 2√𝐷 = 2π‘ž π‘Ž 𝐹𝑛(𝑠, 𝑑) = 2π‘ž π‘Ž 𝐹𝑛 (2 2π‘π‘ž2βˆ’π‘Ž π‘Ž , βˆ’1) = π‘ž 2π‘π‘ž2βˆ’π‘Ž Ψ𝑛 ( 2π‘π‘ž2βˆ’π‘Ž π‘Ž , βˆ’1), For all 𝑛 β‰₯ 1. 4. It is easy to verify (4) from (1). 5. The fifth part can be proved using the theorem. 2.2. Corollary Let 𝐷 = 𝑝2π‘ž2 βˆ’ π‘Žπ‘, with π‘ž > π‘Ž being a multiple of π‘Ž and 𝑝, π‘ž being positive integers chosen in such a way that 𝐷 is not a perfect square, then, the equation π‘₯2 βˆ’ 𝐷𝑦2 = 1 has no positive integer solution. Proof: It is simple to conclude using the theorem..; 2.3. Theorem 1. Let 𝐷 = 𝑝2π‘ž2 + π‘Žπ‘, with π‘ž > π‘Ž being a multiple of π‘Ž and 𝑝, π‘ž being positive integers chosen in such a way that 𝐷 is not a perfect square, then, √𝐷 = βˆšπ‘2π‘ž2 + π‘Žπ‘ = [π‘π‘ž; 2π‘ž π‘Ž , 2π‘π‘ž Μ…Μ… Μ…Μ… Μ…Μ… Μ…Μ… Μ… ]. 2. The fundamental solution of the Pell equation π‘₯2 βˆ’ 𝐷𝑦2 = 1 is (π‘₯1, 𝑦1) = ( 2π‘π‘ž2+π‘Ž π‘Ž , 2π‘ž π‘Ž ). 3. All positive integer solution (π‘₯𝑛, 𝑦𝑛) of the Pell equation π‘₯2 βˆ’ 𝐷𝑦2 = 1 are provided by π‘₯𝑛 = 𝛼𝑛+𝛽𝑛 2 = 1 2 𝐿𝑛(𝑠, 𝑑) = 1 2 𝐿𝑛 (2 2π‘π‘ž2βˆ’π‘Ž π‘Ž , βˆ’1) = 1 2 Ψ𝑛 ( 2π‘π‘ž2βˆ’π‘Ž π‘Ž , βˆ’1), and 𝑦𝑛 = π›Όπ‘›βˆ’π›½π‘› 2√𝐷 = 2π‘ž π‘Ž 𝐹𝑛(𝑠, 𝑑) = 2π‘ž π‘Ž 𝐹𝑛 (2 2π‘π‘ž2+π‘Ž π‘Ž , βˆ’1) = π‘ž 2π‘π‘ž2βˆ’π‘Ž Φ𝑛 (2 2π‘π‘ž2+π‘Ž π‘Ž , βˆ’1), for all 𝑛 β‰₯ 1. 4. The Fundamental solution of Pell equation π‘₯2 βˆ’ 𝐷𝑦2 = π‘˜π‘‘ is (π‘₯1, 𝑦1) = ( 2π‘π‘ž2+π‘Ž π‘Ž π‘˜ 𝑑 2, 2π‘ž π‘Ž π‘˜ 𝑑 2). 5. All positive solutions of Pell equation π‘₯2 βˆ’ 𝐷𝑦2 = π‘˜π‘‘ are given by π‘₯𝑛+1 = 2π‘π‘ž2 + π‘Ž π‘Ž π‘˜ 𝑑 2π‘₯𝑛 + 2π‘ž 𝑝2π‘ž2 + π‘Žπ‘ π‘Ž π‘˜ 𝑑 2𝑦𝑛 and 𝑦𝑛+1 = 2π‘ž π‘Ž π‘˜ 𝑑 2π‘₯𝑛 + 2π‘π‘ž2 + π‘Ž π‘Ž π‘˜ 𝑑 2𝑦𝑛 for all 𝑛 β‰₯ 1. Proof: The proof is similar to theorem 1. 4413 Edelweiss Applied Science and Technology ISSN: 2576-8484 Vol. 8, No. 6: 4408-4414, 2024 DOI: 10.55214/25768484.v8i6.2965 Β© 2024 by the authors; licensee Learning Gate 3. Applications One application of our results is to find the units of β„€[√𝐷]. The unity, in𝑐, is 1and units are those invertible elements. In the following, we will find units of β„€[√𝐷], where 𝐷 = 𝑝2π‘ž2 Β± π‘Žπ‘, with π‘ž > π‘Ž being a multiple of π‘Ž and 𝑝, π‘ž being positive integers chosen in such a way that 𝐷 is not a perfect square. Let 𝑒 + π‘£βˆšπ·, where 𝑒, 𝑣 ∈ β„€ be a unit element in β„€[√𝐷], then there exists some 𝑐 + π‘‘βˆšπ· ∈ β„€[√𝐷] such that (𝑒 + π‘£βˆšπ·)(𝑐 + π‘‘βˆšπ·) = 1. So, 𝑐 + π‘‘βˆšπ· = 1 𝑒+π‘£βˆšπ· = π‘’βˆ’π‘£βˆšπ· 𝑒2βˆ’π‘£2𝐷 , then if we consider the quantity 𝑁(𝑒 + π‘£βˆšπ·) = 𝑒2 βˆ’ 𝑣2𝐷, one can verify that 𝑁 is multiplicative, and then if 𝑒 + π‘£βˆšπ· is invertible, 𝑁 must be invertible too, so it is either 1 or βˆ’1. Then, we get 𝑒2 βˆ’π·π‘£2 = Β±1. Further 𝑒2 βˆ’π·π‘£2 = βˆ’1 has no positive solution. To solve 𝑒2 βˆ’ 𝐷𝑣2 = 1, we apply our theorems. Let for example, 𝑝 = 2, π‘ž = 14, π‘Ž = 7, then 𝐷 = 22(14)2 βˆ’ 7.14 = 686 which is, clearly, not a perfect square. Fundamental solution of π‘₯2 βˆ’ 868𝑦2 = 1 is ( 2.2(14)2βˆ’7 7 , 2.14 7 ) = (195,4). All positive integer solutions of π‘₯2 βˆ’ 868𝑦2 = 1 are { π‘₯𝑛 = 1 2 𝐿𝑛(390,βˆ’1) = 1 2 Ψ𝑛(195,βˆ’1) 𝑦𝑛 = 4𝐹𝑛(390,βˆ’1) = 1 195 Φ𝑛(195,βˆ’1). We will then be required to find 𝐹𝑛 and 𝐿𝑛 for all 𝑛 > 1. Let { 𝐿𝑛(390,βˆ’1) = 390 Lπ‘›βˆ’1(390,βˆ’1) βˆ’ Lπ‘›βˆ’2(390,βˆ’1), βˆ€ 𝑛 > 2, 𝐿0(390,βˆ’1) = 2, 𝐿1(390,βˆ’1) = 390 𝐹𝑛(390,βˆ’1) = 390 Fπ‘›βˆ’1(390,βˆ’1) βˆ’ πΉπ‘›βˆ’2(390,βˆ’1) βˆ€ 𝑛 > 2, 𝐹0(390,βˆ’1) = 0, 𝐹1(390,βˆ’1) = 1 So, 195 + 4√686 $195+4 is a unit of β„€[√686]. As 𝐿2(390,βˆ’1) = 152098 and 𝐹2(390,βˆ’1) = 390, then 76049 + 1560√686 is another unit of β„€[√686], and so on. We can clearly express units of β„€[√686] in terms of generalized Fibonacci, generalized Lucas, generalized Pell, and generalized Pell- Lucas numbers. 4. Conclusion The Diophantine equation π‘₯2 βˆ’ (𝑝2π‘ž2 Β± π‘Žπ‘)𝑦2 = π‘˜π‘‘ has been solved, and its positive integer solutions have been stated in terms of generalized Fibonacci, generalized Lucas, generalized Pell, and generalized Pell-Lucas sequences. 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