Arithmetic properties and asymptotic formulae for ${\sigma }_o\text{mex}(n)$ and ${\sigma }_e\text{mex}(n)$

Abstract

The minimal excludant of an integer partition is the least positive integer missing from the partition. Let ${\sigma }_o\text{mex}(n)$ (resp., ${\sigma }_e\text{mex}(n)$) denote the sum of odd (resp., even) minimal excludants over all the partitions of $n$. Recently, Baruah et al. proved a few congruences for these partition functions modulo $4$ and $8$, and asked for asymptotic formulae for the same. In this article, we study the lacunarity of ${\sigma }_o\text{mex}(n)$ and ${\sigma }_e\text{mex}(n)$ modulo arbitrary powers of $2$ and also prove some infinite families of congruences for ${\sigma }_o\text{mex}(n)$ and ${\sigma }_e\text{mex}(n)$ modulo $4$ and $8$. We also obtain Hardy-Ramanujan type asymptotic formulae for both ${\sigma }_o\text{mex}(n)$ and ${\sigma }_e\text{mex}(n)$.

15 pages