What is the next number in the sequence
Computer Science
Level
2
- 1
- 11
- 21
- 1211
- 111221
- ?
The answer is 312211.
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1 solution
This is the Look-and-say sequence. To generate a member of the sequence from the previous member, read off the digits of the previous member, counting the number of digits in groups of the same digit. For example:
1 is read off as "one 1" or 11. 11 is read off as "two 1s" or 21. 21 is read off as "one 2, then one 1" or 1211. 1211 is read off as "one 1, one 2, then two 1s" or 111221. 111221 is read off as "three 1s, two 2s, then one 1" or 312211. The look-and-say sequence was introduced and analyzed by John Conway .
The idea of the look-and-say sequence is similar to that of run-length encoding .