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 A143477 #6 Jan 16 2013 18:52:11 %S A143477 1,2,2,2,1,1,2,2,1,2,1,1,2,2,2,1,1,2,1,2,2,1,1,1,1,2,1,2,2,1,2,2,1,1, %T A143477 2,1,2,1,2,2,1,2,2,1,1,2,1,1,2,2,1,2,1,1,2,2,2,1,2,2,1,1,2,1,1,2,2,1, %U A143477 2,1,1,2,1,2,2,1,1,2,1,1,2,1,2,2,1,1,2,2,1,2,2,1,1,2,1,2,2,1,2,1,1,2,2,1,2 %N A143477 Kolakoski Fan. %C A143477 (1) Does every row occur infinitely many times as a segment of A000002? %C A143477 (2) In Kolakoski's note, the initial 1 appears at the bottom, centered, with 2 just above and successive rows arise as branches so that the array resembles a handheld fan. %C A143477 Arises from the Kolakoski sequence, K(n)=A000002(n), as follows: %C A143477 row 1: 1 %C A143477 row 2: 2 %C A143477 row 3: 2 2 %C A143477 row 4: 1 1 2 2 %C A143477 row 5: 1 2 1 1 2 2, %C A143477 and so on, where the first term in row n is K(n) and row n-1 tells how many of each kind (1 or 2) to write in row n. %D A143477 William G. Kolakoski, unpublished note entitled "Kolakoski Series Fan," dated Nov 12, 1993. %H A143477 Wikipedia, <a href="http://en.wikipedia.org/wiki/Kolakoski_sequence">Kolakoski sequence</a> %e A143477 Row 4 (1,1,2,2) determines row 5: (one 1, one 2, two 1's, two 2's). %Y A143477 Cf. A000002. %K A143477 nonn,tabl %O A143477 1,2 %A A143477 _Clark Kimberling_, Aug 19 2008, Aug 25 2008