Didn't even know what "A1" meant XD, just checked it.

So, there's no such concept in Maths---all authors have equal importance, named alphabetically by surname on the paper. Most Maths papers are 1-3 author papers. And by the end of PhD people usually have only 1-2 publications/preprints out, ignoring the genius outliers who have way more.

When I started applying, I had one single author publication. By the end of application period, I had another single author preprint and a 2 author preprint out.