$a$-Numbers of Cyclic Degree $p^2$ Covers of the Projective Line

We investigate the $a$-numbers of $\mathbb{Z}\mathrm{/}{p}^2\mathbb{Z}$-covers in characteristic $p>2$ and extend a technique originally introduced by Farnell and Pries for $\mathbb{Z}\mathrm{/}p\mathbb{Z}$-covers. As an application of our approach, we demonstrate that the $a$-numbers of ``minimal’’ $\mathbb{Z}\mathrm{/}9\mathbb{Z}$-covers can be deduced from the associated branching datum.