mchirico: I believe the answer might be 312211
reasoning:
start with 1
1
each following sequence describes the pattern before it:
1 1 = 11
2 1's = 21
1 2 and 1 1 = 1211
1 1, 1 2, and 2 1's = 111221
3 1's, 2 2's, and 1 1 = 312211 (answer)
following that, we'd have:
1 3, 1 1, 2 2's, and 2 1's = 13112221
etc