What's the next in the series

1, 11, 21, 1211, 3112, 132112, __________

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Next number is 311322 (or three 1's, one 3, two 2's - the numbers in the previous number).

Total sequence is:
1 - START
11 = one 1
21 = two 1's
1211 = one 2, one 1
3112 = three 1's, one 2
132112 = one 3, two 1's, one 2
soooo...
311322 = three 1's, one 3, two 2's