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 A256138 #29 Mar 29 2015 23:08:37 %S A256138 1,5,9,21,25,37,57,85,89,101,121,157,193,221,273,333,337,349,369,405, %T A256138 441,477,545,645,713,741,793,885,993,1069,1193,1317,1321,1333,1353, %U A256138 1389,1425,1461,1529,1629,1697,1733,1801,1917,2065,2197,2361,2589,2721,2749,2801,2893,3001,3109,3281,3549,3785,3893,4017,4237,4513,4709,4985,5237 %N A256138 Total number of ON states after n generations of cellular automaton of A151723 based on hexagons, if we only look at two opposite 120-degree wedges, including the central cell. %C A256138 First differs from both A169707 and A246335 at a(12). %C A256138 First differs from the average of A169707 and A246335 at a(13). %C A256138 Note that the above mentioned cellular automata work on the square grid. %C A256138 A256139 gives the number of cells turned ON at the n-th stage. %H A256138 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 A256138 <a href="/index/Ce#cell">Index entries for sequences related to cellular automata</a> %F A256138 a(n) = 1 + 2*(A151723(n) - 1)/3 = 1 - 4*n + 4*A169780(n). %F A256138 a(n) = 1 + 4*A169779(n-2), n >= 2. %F A256138 a(n) = A151723(n) - 2*A169779(n-2), n >= 2. %Y A256138 Cf. A151723, A169707, A169779, A169780, A170898, A246333, A246335, A256139. %K A256138 nonn %O A256138 1,2 %A A256138 _Omar E. Pol_, Mar 20 2015