Look and Say sequence
Known as: Look and Say sequence
Each term is a verbal description of the previous term's digits.
For example, the sixth term describes the fifth term as "three ones, two twos, and one one".
The first 11 terms (starting from n=1) are:
1 11 21 1211 111221 312211 13112221 1113213211 13211311123113112211 11131221133112132113212221 3113112221232112111312211312113211