This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A111081 #5 Mar 30 2012 18:39:24 %S A111081 1,2,11,21,221,22112,11221211,21221121121,2212211212212112, %T A111081 1122122112122122112112122,12112212211212212211211221211212212211, %U A111081 211212211211221211211221221121221211221221211211221221121 %N A111081 Successive generations of an alternating Kolakoski rule. %C A111081 Strings are obtained using the Kolakoski substitution and the additional rule : start with 1 if previous string ends with 2, start with 2 if previous string ends with 1. The concatenation of those strings gives 1211212212211211221211...which is A006928 word. If you replace the initial 1 with 12 you get 122112122122112112212...the infinite Kolakoski word A000002. %F A111081 Conjecture : length of n-th string is asymptotic to c*(3/2)^n for some c. %e A111081 1-->2-->11-->21-->221-->22112-->11221211 %Y A111081 Cf. A000002, A054349. %K A111081 nonn,base %O A111081 1,2 %A A111081 _Benoit Cloitre_, Oct 11 2005