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p-Adic quotient sets: Linear recurrence sequences with reducible characteristic polynomials

Published online by Cambridge University Press:  11 December 2024

Deepa Antony
Affiliation:
Department of Mathematics, Indian Institute of Technology Guwahati, Guwahati, Assam, India, 781039 e-mail: deepa172123009@iitg.ac.in
Rupam Barman*
Affiliation:
Department of Mathematics, Indian Institute of Technology Guwahati, Guwahati, Assam, India, 781039 e-mail: deepa172123009@iitg.ac.in
*

Abstract

Let $(x_n)_{n\geq 0}$ be a linear recurrence sequence of order $k\geq 2$ satisfying

$$ \begin{align*}x_n=a_1x_{n-1}+a_2x_{n-2}+\dots+a_kx_{n-k}\end{align*} $$
for all integers $n\geq k$, where $a_1,\dots ,a_k,x_0,\dots , x_{k-1}\in \mathbb {Z},$ with $a_k\neq 0$. In 2017, Sanna posed an open question to classify primes p for which the quotient set of $(x_n)_{n\geq 0}$ is dense in $\mathbb {Q}_p$. In a recent paper, we showed that if the characteristic polynomial of the recurrence sequence has a root $\pm \alpha $, where $\alpha $ is a Pisot number and if p is a prime such that the characteristic polynomial of the recurrence sequence is irreducible in $\mathbb {Q}_p$, then the quotient set of $(x_n)_{n\geq 0}$ is dense in $\mathbb {Q}_p$. In this article, we answer the problem for certain linear recurrence sequences whose characteristic polynomials are reducible over $\mathbb {Q}$.

Information

Type
Article
Copyright
© The Author(s), 2024. Published by Cambridge University Press on behalf of Canadian Mathematical Society

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