Finite $p$-groups all of whose subgroups of index $p^3$ are abelian

Abstract: Suppose that $G$ is a finite $p$-group. If all subgroups of index $p<sup>t$ of $G$ are abelian and at least one subgroup of index $p<sup>{t-1}$ of $G$ is not abelian, then $G$ is called an $\mathcal{A}_t$-group. In this paper, some information about $\mathcal{A}_t$-groups are obtained and $\mathcal{A}_3$-groups are completely classified. This solves an {\it old problem} proposed by Berkovich and Janko in their book. Abundant information about $\mathcal{A}_3$-groups are given.