What's the sequence?

Question

1
11
21
1211
111221

Answer 1

312211
13112221
1113213211
...

the last line means: "one 1, one 3, two 1s, three 2s, one 1"
which describes the second last line: 1 - 3 - 11 - 222 - 1

Answer 2

A005150 Look and Say sequence: describe the previous term! (method A - initial term is 1).
(Formerly M4780)

COMMENT Method A = 'frequency' followed by 'digit'-indication.
Only the digits 1, 2 and 3 appear in any term. - Robert G. Wilson v Jan 22 2004.

for future reference if you get stuck on a sequence you can always try a lookup at the link below.

Answer 3

i am Souf not hassan h:

the next number of the sequence is: 312211