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 A267447 #12 Feb 16 2025 08:33:29
%S A267447 0,3,4,7,4,8,8,15,4,8,8,16,8,16,16,31,4,8,8,16,8,16,16,32,8,16,16,32,
%T A267447 16,32,32,63,4,8,8,16,8,16,16,32,8,16,16,32,16,32,32,64,8,16,16,32,16,
%U A267447 32,32,64,16,32,32,64,32,64,64,127,4,8,8,16,8,16,16
%N A267447 Number of OFF (white) cells in the n-th iteration of the "Rule 129" elementary cellular automaton starting with a single ON (black) cell.
%D A267447 S. Wolfram, A New Kind of Science, Wolfram Media, 2002; p. 55.
%H A267447 Robert Price, <a href="/A267447/b267447.txt">Table of n, a(n) for n = 0..1000</a>
%H A267447 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/ElementaryCellularAutomaton.html">Elementary Cellular Automaton</a>
%H A267447 S. Wolfram, <a href="http://wolframscience.com/">A New Kind of Science</a>
%H A267447 <a href="/index/Ce#cell">Index entries for sequences related to cellular automata</a>
%H A267447 <a href="https://oeis.org/wiki/Index_to_Elementary_Cellular_Automata">Index to Elementary Cellular Automata</a>
%F A267447 Conjecture: a(n) = A071051(n), n>0. - _R. J. Mathar_, Jan 17 2016
%t A267447 rule=129; rows=20; ca=CellularAutomaton[rule,{{1},0},rows-1,{All,All}]; (* Start with single black cell *) catri=Table[Take[ca[[k]],{rows-k+1,rows+k-1}],{k,1,rows}]; (* Truncated list of each row *) nbc=Table[Total[catri[[k]]],{k,1,rows}]; (* Number of Black cells in stage n *) Table[Length[catri[[k]]]-nbc[[k]],{k,1,rows}] (* Number of White cells in stage n *)
%Y A267447 Cf. A267417.
%K A267447 nonn,easy
%O A267447 0,2
%A A267447 _Robert Price_, Jan 15 2016