Math puzzles!

And BULLSEYE! *ba dum tch*
that is indeed correct~ you can just triple 60 your way to anything before 159 by taking 99 and before for the last two darts. Excellent intuition! THIS IS THE TRUE ESSENCE OF MATH MUHAHAHAHAAHA! *cough* ahem~

12) Continue the sequence (If you've seen it, let everyone else suffer):

[just give me the next line]
1
11
21
1211
111221
312211
...?

13112221