Which number comes next?

1

11

21

1211

111221

312211

13112221

1113213211

Answer –  31131211131221

Reason –  If you say it out loud, for the first one, there is one 1. So it is 11. There are two ones in 11. So that makes it 21. There is one 2 and one 1 in 21, which makes it 1211. There’s one 1, one 2, and two 1’s, making it 111221. If you continue this pattern to the last number (1113213211) there are three 1’s, one 3, one 2, one 1, one 3, one 2, and two 1’s, which is 31131211131221. 

Cites 

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