This question was motivated by Martin's comment in Free $\mathbb{Z}_2$-actions match at some point

When was the notation $\mathbb Z_n$ introduced for $n$-adic integers and by whom? When was it introduced for integers modulo $n$ and by whom?

I tried searching on Google without much luck.

Added. Martin brings up the related point when was the subscript notation $A_f$ introduced for localizing a ring at the monoid generated by $f$ (which is a third possible interpretation of $\mathbb Z_n$)?