On finitely many base $q$ expansions

Abstract

Given some integer $m\ge 3$, we find the first explicit collection of countably many intervals in $(1,2)$ such that for any $q$ in one of these intervals, the set of points with exactly $m$ base $q$ expansions is nonempty and moreover has positive Hausdorff dimension. Our method relies on an application of a theorem proved by Falconer and Yavicoli, which guarantees that the intersection of a family of compact subsets of ${\mathbb{R}}^d$ has positive Hausdorff dimension under certain conditions.