Rationality of the zeta function of the subgroups of abelian $p$-groups

Abstract

Given a finite abelian $p$-group $F$, we prove an efficient recursive formula for ${\sigma }_a(F)={\sum }_{\begin{array}{c}H\le F\end{array}}|H{|}^a$ where $H$ ranges over the subgroups of $F$. We infer from this formula that the $p$-component of the corresponding zeta-function on groups of $p$-rank bounded by some constant $r$ is rational with a simple denominator. We also provide two explicit examples in rank $r=3$ and $r=4$ as well as a closed formula for ${\sigma }_a(F)$.