[DanielStraight]

I have no answer for you. I mean... the solution seems to be 2121 or 2122 (no, it isn't, see below) determined by brute force, but I don't know why.

But, it's worth noting that if this interests you, Project Euler almost certainly will as well and is worth checking it out if you don't already know about it:

http://projecteuler.net/

EDIT: So if you're wondering why I got a different brute force result from other users, it's because I had a stupid bug. I was looking at the ratio of meeting the criteria to the ratio of not meeting it, not the ratio of meeting it to total.