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 A262621 #15 Nov 25 2015 02:33:31 %S A262621 1,4,12,4,28,20,12,4,60,52,44,36,28,20,12,4,124,116,108,100,92,84,76, %T A262621 68,60,52,44,36,28,20,12,4,252,244,236,228,220,212,204,196,188,180, %U A262621 172,164,156,148,140,132,124,116,108,100,92,84,76,68,60,52,44,36,28,20,12,4,508,500,492,484,476,468,460,452,444,436 %N A262621 First differences of A262620. %C A262621 Number of cells turned "ON" at n-th stage of cellular automaton of A262620. %H A262621 N. J. A. Sloane, <a href="/wiki/Catalog_of_Toothpick_and_CA_Sequences_in_OEIS">Catalog of Toothpick and Cellular Automata Sequences in the OEIS</a> %H A262621 <a href="/index/Ce#cell">Index entries for sequences related to cellular automata</a> %F A262621 a(n) = 4 * A261693(n), n >= 1. %e A262621 With the terms written as an irregular triangle in which row lengths are the terms of A011782 the sequence begins: %e A262621 1; %e A262621 4; %e A262621 12, 4; %e A262621 28, 20, 12, 4; %e A262621 60, 52, 44, 36, 28, 20, 12, 4; %e A262621 124, 116, 108, 100, 92, 84, 76, 68, 60, 52, 44, 36, 28, 20, 12, 4; %e A262621 ... %Y A262621 Cf. A147582, A160721, A261693, A262620. %Y A262621 Row sums give A000302. Row lengths give A011782. Right border gives A123932. Column 1 is A173033. %K A262621 nonn,tabf %O A262621 0,2 %A A262621 _Omar E. Pol_, Nov 03 2015