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Published online by Cambridge University Press: 06 October 2025
Let $\{u_n\}_n$ be a nondegenerate linear recurrence sequence of integers with Binet’s formula given by
${u_n= \sum _{i=1}^{m} P_i(n)\alpha _i^n.}$ Assume
$\max _i \vert \alpha _i \vert>1$. In 1977, Loxton and Van der Poorten conjectured that for any
$\epsilon>0$, there is an effectively computable constant
$C(\epsilon )$ such that if
$ \vert u_n \vert < (\max _i\{ \vert \alpha _i \vert \})^{n(1-\epsilon )}$, then
$n<C(\epsilon )$. Using results of Schmidt and Evertse, a complete noneffective (qualitative) proof of this conjecture was given by Fuchs and Heintze [‘On the growth of linear recurrences in function fields’, Bull. Aust. Math. Soc. 104(1) (2021), 11–20] and, independently, by Karimov et al. [‘The power of positivity’, Proc. LICS 23 (2023), 1–11]. In this paper, we give an effective upper bound for the number of solutions of the inequality
$\vert u_n \vert < (\max _i\{ \vert \alpha _i \vert \})^{n(1-\epsilon )}$, thus extending several earlier results by Schmidt, Schlickewei and Van der Poorten.
Communicated by Dmitry Badziahin
This research was funded in whole or in part by Austrian Science Fund (FWF): I4406.