ON THE DENSITY OF SUMSETS, II

Abstract

AbstractArithmetic quasidensities are a large family of real-valued set functions partially defined on the power set of $\mathbb {N}$ , including the asymptotic density, the Banach density and the analytic density. Let $B \subseteq \mathbb {N}$ be a nonempty set covering $o(n!)$ residue classes modulo $n!$ as $n\to \infty $ (for example, the primes or the perfect powers). We show that, for each $\alpha \in [0,1]$ , there is a set $A\subseteq \mathbb {N}$ such that, for every arithmetic quasidensity $\mu $ , both A and the sumset $A+B$ are in the domain of $\mu $ and, in addition, $\mu (A + B) = \alpha $ . The proof relies on the properties of a little known density first considered by Buck [‘The measure theoretic approach to density’, Amer. J. Math.68 (1946), 560–580].