Published online by Cambridge University Press: 29 November 2017
Let $S=\{q_{1},\ldots ,q_{s}\}$ be a finite, non-empty set of distinct prime numbers. For a non-zero integer
$m$ , write
$m=q_{1}^{r_{1}}\cdots q_{s}^{r_{s}}M$ , where
$r_{1},\ldots ,r_{s}$ are non-negative integers and
$M$ is an integer relatively prime to
$q_{1}\cdots q_{s}$ . We define the
$S$ -part
$[m]_{S}$ of
$m$ by
$[m]_{S}:=q_{1}^{r_{1}}\cdots q_{s}^{r_{s}}$ . Let
$(u_{n})_{n\geqslant 0}$ be a linear recurrence sequence of integers. Under certain necessary conditions, we establish that for every
$\unicode[STIX]{x1D700}>0$ , there exists an integer
$n_{0}$ such that
$[u_{n}]_{S}\leqslant |u_{n}|^{\unicode[STIX]{x1D700}}$ holds for
$n>n_{0}$ . Our proof is ineffective in the sense that it does not give an explicit value for
$n_{0}$ . Under various assumptions on
$(u_{n})_{n\geqslant 0}$ , we also give effective, but weaker, upper bounds for
$[u_{n}]_{S}$ of the form
$|u_{n}|^{1-c}$ , where
$c$ is positive and depends only on
$(u_{n})_{n\geqslant 0}$ and
$S$ .