need help with this number this

13112221

1 (one 1)
1 1 (two 1's)
2 1 <---- Missing Line (one 2, one 1)
1 2 1 1 (one 1, one 2, two 1)
1 1 1 2 2 1 (three 1, two 2, one 1)
3 1 2 2 1 1 (one 3, one 1, two 2, two 1)
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1 3 1 1 2 2 2 1 (one 1, one 3, two 1, three 2, one 1)
1 1 1 3 2 1 3 2 1 1 (three 1, one 3, one 2, one 1, one 3, one 2, two 1)

*Count how many of each number there are in a row then say how many there are. Convert the word into numbers (eg. 112: two 1, one 2 = 2112)