I signed up sometime last week to check it out, and my six-digit bank account ID numbers in Mint's database are 6079xx and 6079xx+1. They're sequential, so there are 600,000ish rows in the table, but that's not necessarily proof that they're all active.
I don't use Mint for anything really, but technically I'm a user.
Mint's user data is sharded across multiple DB's. So if you're the first user on a fresh DB, your bank account will have ID 1. Also, users usually have multiple bank accounts as well, so accountId isn't a good indicator of # of users.
I don't use Mint for anything really, but technically I'm a user.