Regular expression for at least n digits anywhere in the string?

A regular expression for at least one digit in a string looks like this:

(?=.*[0-9]) 

So that would find a1a or a2a2 etc.

Suppose we wanted at least 2 digits in the string. So it should return true for a2a2 or a2a2a2, but a2 would not pass.

What would that regex look like?