Solution to: Strange Sequence

The system behind the sequence is that each number (except the first one of the sequence) "describes" the previous number. So 11 means one "1", 21 means two times a "1", 1211 means one "2" and one "1", and 111221 means one "1", one "2", and two times a "1". The number following on 111221 is therefore 312211 (three times a "1", two times a "2", and one "1").

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