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 A256139 #15 Mar 29 2015 23:08:45 %S A256139 1,4,4,12,4,12,20,28,4,12,20,36,36,28,52,60,4,12,20,36,36,36,68,100, %T A256139 68,28,52,92,108,76,124,124,4,12,20,36,36,36,68,100,68,36,68,116,148, %U A256139 132,164,228,132,28,52,92,108,108,172,268,236,108,124,220,276,196,276,252 %N A256139 First differences of A256138. %C A256139 Number of cells turned ON at n-th stage in the structure of A256138. %C A256139 First differs from A169708 at a(11). %H A256139 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 A256139 <a href="/index/Ce#cell">Index entries for sequences related to cellular automata</a> %F A256139 a(n) = 2*A151724(n+1)/3, n >= 1. %e A256139 Written as an irregular triangle in which the row lengths are the terms of A011782 the sequence begins: %e A256139 1; %e A256139 4; %e A256139 4,12; %e A256139 4,12,20,28; %e A256139 4,12,20,36,36,28,52,60; %e A256139 4,12,20,36,36,36,68,100,68,28,52,92,108,76,124,124; %e A256139 4,12,20,36,36,36,68,100,68,36,68,116,148,132,164,228,132,28,52,92,108,108,172,268,236,108,124,220,276,196,276,252; %e A256139 ... %e A256139 It appears that the right border gives A173033. %Y A256139 Cf. A028399, A011782, A151723, A151724, A160721, A169708, A170898, A170905, A173033, A256138. %K A256139 nonn,tabf %O A256139 0,2 %A A256139 _Omar E. Pol_, Mar 20 2015