Solution to: Strange Sequence

The system behind the sequence is that each number, except the first, describes the preceding number by reading its digits from left to right.

Thus, 11 means: one 1.
21 means: two times a 1.
1211 means: one 2 and one 1.
111221 means: one 1, one 2, and two times a 1.

Therefore, the number after 111221 is 312211: three times a 1, two times a 2, and one 1.

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