title: Finding the largest modulus of congruence for two integers?
body: <p>Given two integers is there an easy way to find the largest modulus of congruence for them? i.e. a % n == b %n, Or even to enumerate all of them?  Obviously, I could try every value less than them, but it seems like there should be an easier way.</p>
  
  <p>I tried doing something with gcds, but then you just get things where a % n == b % n == 0, which isn't as cool as I was hoping for, and I'm pretty sure this isn't necessarily the largest n.</p>
  
  <p>Any ideas?</p>