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 A253079 #17 Feb 14 2015 21:51:55
%S A253079 1,5,13,17,33,21,65,65,97,61,145,153,177,149,257,249,345,237,433,409,
%T A253079 465,389,601,521,745,501,897,713,897,709,1081,921,1281,877,1481,1121,
%U A253079 1505,1125,1817,1393,1993,1309,2209,1577,2401,1653,2497,1953,2985,1901
%N A253079 a(n) = if n is even, number of ON cells at stage n of two-dimensional 5-neighbor outer totalistic cellular automaton defined by "Rule 489" or if n is odd, number of OFF cells.
%C A253079 If we subtract 1 and divide by 4, the result (A253080) almost looks like it should have a simple recurrence. It would be nice to know more.
%D A253079 S. Wolfram, A New Kind of Science, Wolfram Media, 2002; pp. 173-175.
%H A253079 N. J. A. Sloane, <a href="/A253079/a253079.png">Illustration of generations 0-23</a>
%H A253079 <a href="/index/Ce#cell">Index entries for sequences related to cellular automata</a>
%t A253079 Map[Function[Apply[Plus, Flatten[ #1]]], CellularAutomaton[{ 489, {2, {{0, 2, 0}, {2, 1, 2}, {0, 2, 0}}}, {1, 1}}, {{{1}}, 0}, 200]] (* then subtract the odd-indexed terms from 201^2 (a constant which depends on Mathematica's choice of grid size) *)
%t A253079 ArrayPlot /@ CellularAutomaton[{489, {2, {{0, 2, 0}, {2, 1, 2}, {0, 2, 0}}}, {1, 1}}, {{{1}}, 0}, 23]
%Y A253079 Cf. A253080, A169699, A246316, A246318, A246325, A246326, ...
%K A253079 nonn
%O A253079 0,2
%A A253079 _N. J. A. Sloane_, Feb 04 2015