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arXiv · 1803.10434

On the $x$--coordinates of Pell equations which are $k$--generalized Fibonacci numbers

Mahadi Ddamulira·Florian Luca
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Abstract

For an integer $k\geq 2$, let $\{F^{(k)}_{n}\}_{n\geqslant 2-k}$ be the $ k$--generalized Fibonacci sequence which starts with $0, \ldots, 0,1$ (a total of $k$ terms) and for which each term afterwards is the sum of the $k$ preceding terms. In this paper, for an integer $d\geq 2$ which is square free, we show that there is at most one value of the positive integer $x$ participating in the Pell equation $x^{2}-dy^{2} =\pm 1$ which is a $k$--generalized Fibonacci number, with a couple of parametric exceptions which we completely characterise. This paper extends previous work from [17] for the case $k=2$ and [16] for the case $k=3$.

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Mahadi Ddamulira, Florian Luca. 2018-03-28. On the $x$--coordinates of Pell equations which are $k$--generalized Fibonacci numbers. https://arxiv.org/abs/1803.10434

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