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 A267940 #19 Feb 16 2025 08:33:30
%S A267940 1,11,11111,1111111,111111111,11111111111,1111111111111,
%T A267940 111111111111111,11111111111111111,1111111111111111111,
%U A267940 111111111111111111111,11111111111111111111111,1111111111111111111111111,111111111111111111111111111,11111111111111111111111111111
%N A267940 Binary representation of the n-th iteration of the "Rule 253" elementary cellular automaton starting with a single ON (black) cell.
%C A267940 With the exception of a(1) the same as A267937, A267889, A267887 and A100706. - _R. J. Mathar_, Jan 24 2016
%D A267940 S. Wolfram, A New Kind of Science, Wolfram Media, 2002; p. 55.
%H A267940 Robert Price, <a href="/A267940/b267940.txt">Table of n, a(n) for n = 0..1000</a>
%H A267940 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/ElementaryCellularAutomaton.html">Elementary Cellular Automaton</a>
%H A267940 S. Wolfram, <a href="http://wolframscience.com/">A New Kind of Science</a>
%H A267940 <a href="/index/Ce#cell">Index entries for sequences related to cellular automata</a>
%H A267940 <a href="https://oeis.org/wiki/Index_to_Elementary_Cellular_Automata">Index to Elementary Cellular Automata</a>
%F A267940 Conjectures from _Colin Barker_, Jan 23 2016 and Apr 16 2019: (Start)
%F A267940 a(n) = 101*a(n-1)-100*a(n-2) for n>3.
%F A267940 G.f.: (1-90*x+10100*x^2-10000*x^3) / ((1-x)*(1-100*x)).
%F A267940 (End)
%t A267940 rule=253; 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 *) Table[FromDigits[catri[[k]]],{k,1,rows}] (* Binary Representation of Rows *)
%Y A267940 Cf. A060576.
%K A267940 nonn,easy
%O A267940 0,2
%A A267940 _Robert Price_, Jan 22 2016