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 A054349 #20 Apr 13 2020 07:13:33 %S A054349 2,22,2211,221121,221121221,22112122122112,2211212212211211221211, %T A054349 221121221221121122121121221121121, %U A054349 2211212212211211221211212211211212212211212212112 %N A054349 Successive generations of the variant of the Kolakoski sequence described in A042942. %C A054349 For n >= 0, let f_1(n) be the number of 1's in a(n) (sequence begins: 0, 0, 2, 3, 4, 6, 11, 17, 24, ...) and f_2(n) be the number of 2's (sequence begins: 1, 2, 2, 3, 5, 8, 11, 16, 25, ...). Then there is a simple relation between f_1 and f_2, namely: f_1(n) = 1 - f_2(n) + f_2(n-1) + f_2(n-2) + ... + f_2(0). i.e. f_1(7) = 17 and 1 - f_2(7) + f_2(6) + ... + f_2(0) = 1 - 16 + 11 + 8 + 5 + 3 + 2 + 2 + 1 = 17. - _Benoit Cloitre_, Oct 11 2005 %H A054349 Bertran Steinsky, <a href="https://cs.uwaterloo.ca/journals/JIS/VOL9/Steinsky/steinsky5.html">A Recursive Formula for the Kolakoski Sequence A000002</a>, J. Integer Sequences, Vol. 9 (2006), Article 06.3.7. %Y A054349 Cf. A000002, A054348, A054350, A054351, A111123, A111124. %Y A054349 Word lengths give A042942. %K A054349 nonn,easy %O A054349 0,1 %A A054349 _N. J. A. Sloane_, May 07 2000 %E A054349 More terms from _David Wasserman_, Mar 04 2002