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 A158772 #3 Mar 30 2012 18:52:03 %S A158772 21,21,21,42,42,42,84,84,84,168,168,168,336,336,336,672,672,672,1344, %T A158772 1344,1344,2688,2688,2688,5376,5376,5376,10752,10752,10752,21504, %U A158772 21504,21504,43008,43008,43008,86016,86016,86016,172032,172032,172032,344064 %N A158772 a(n) = A138635(n+18)-A138635(n). %C A158772 a(n) divided by 21 is the sequence 1,1,1,2,2,2,4,4,4,.., that is A000079 triplicated. %K A158772 nonn,less %O A158772 0,1 %A A158772 _Paul Curtz_, Mar 26 2009 %E A158772 Edited by _R. J. Mathar_, May 17 2009