1, 11, 21, 1211, 111221

[jeffrallen]

Complete the series. CliffStoll says on page 313 of the Cuckoo's Egg that he didn't get it at NSA. Do you know it now, Cliff?

[sverona]

My favorite thing about the look-and-say sequence [0] is that John Conway completely characterized it in a 1986 paper. The sequence can be compressed into atomic subsequences that evolve separately. There are 92 of them. So he named them after the elements. They "decay" into other elements. It seems that anything he touches gets its own cute little flair (see for instance the vast number of Life patterns with cute, evocative names.) Rest in peace.

[0] https://en.wikipedia.org/wiki/Look-and-say_sequence

[emdashcomma]

My geometry teacher gave this to the class in high school. I love this sequence.

[kohlschuetter]

Without the next element of the "Look-and-say sequence", 312211, for the example in the title there can also be rules that yield 111111211, or one of: (221211, 111211, 121211, 211211)

[quietthrow]

312211

[addcommitpush]

312211

[selectnull]

13112221

[dcminter]

Similar in nature:

3, 3, 5, 4, 4, 3, 5, ...