On mex-related partition functions of Andrews and Newman

Abstract

The minimal excludant, or “mex” function, on a set S of positive integers is the least positive integer not in S. In a recent paper, Andrews and Newman extended the mex-function to integer partitions and found numerous surprising partition identities connected with these functions. Very recently, da Silva and Sellers present parity considerations of one of the families of functions Andrews and Newman studied, namely $p_{t,t}(n)$, and provide complete parity characterizations of $p_{1,1}(n)$ and $p_{3,3}(n)$. In this article, we study the parity of $p_{t,t}(n)$ when $t=2^{\alpha }, 3\cdot 2^{\alpha }$ for all $\alpha \ge 1$. We prove that $p_{2^{\alpha },2^{\alpha }}(n)$ and $p_{3\cdot 2^{\alpha }, 3\cdot 2^{\alpha }}(n)$ are almost always even for all $\alpha \ge 1$. Using a result of Ono and Taguchi on nilpotency of Hecke operators, we also find infinite families of congruences modulo 2 satisfied by $p_{2^{\alpha },2^{\alpha }}(n)$ and $p_{3\cdot 2^{\alpha }, 3\cdot 2^{\alpha }}(n)$ for all $\alpha \ge 1$.