Look-and-say sequence

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The Look and say sequence is a recursively defined sequence of numbers.

Sequence Definition

  • Take a decimal number
  • Look at the number, visually grouping consecutive runs of the same digit.
  • Say the number, from left to right, group by group; as how many of that digit there are - followed by the digit grouped.

This becomes the next number of the sequence.

An example:

  • Starting with the number 1, you have one 1 which produces 11
  • Starting with 11, you have two 1's. I.E.: 21
  • Starting with 21, you have one 2, then one 1. I.E.: (12)(11) which becomes 1211
  • Starting with 1211, you have one 1, one 2, then two 1's. I.E.: (11)(12)(21) which becomes 111221

Test

{{test}}

Console output