Integers in Sequences Generated by Recurrences with Non-Integer Coefficients

Abstract

In this paper, we study the properties of linear second-order recurrences whose coefficients are non-integer rational numbers. We examine the set of indices at which the terms in the sequence are integers. Specifically, we prove two results. First, after fixing coefficients to satisfy certain coprimality assumptions, we show that there exist coprime integer initial conditions so that the set of integer terms of that sequence is as large as desired. Second, using the same coprimality assumptions, for each fixed pair of initial conditions, we give an explicit cutoff index after which no further terms are integral.