Here's a #Python script you can run on Python-Fiddle to fetch your followers and display how many of them are in each instance: https://python-fiddle.com/saved/R46n7IEdrUps0prVY128

Looks like this for me:

Total followers retrieved: 585
585 accounts in 175 instances.
121 single accounts in a instance.

Follower accounts per instance:
mastodon.social: 157
fosstodon.org: 82
hachyderm.io: 26
ursal.zone: 24
bolha.one: 12
mstdn.social: 12
bolha.us: 11
mastodon.online: 7
tech.lgbt: 6
bertha.social: 6
infosec.exchange: 6
[...]