Originally posted by royalchickenHmm, too easy
Just a guess: each term describes the number of times each digit appears in the previous term, with the exception of the first term, which is defined as 1?
11 (one one)
21 (two ones)
1211 (one two, one one)
111221 (one one, one two, two ones)
Interestingly, I don't think it is possible to ever get a four to appear here. Does that sound right?