Let $a_n$ be a sequence of natural numbers defined by $a_1 = m$ and for $n > 1$. We call apair$ (a_k, a_{\ell })$ interesting if (i) $0 < \ell - k < 2016$, (ii) $a_k$ divides $a_{\ell }$. Show that there exists a $m$ such that the sequence $a_n$ contains no interesting pair.
Problem
Source: Switzerland - 2016 Swiss MO Final Round p6
Tags: number theory, Sequence, recurrence relation