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 A266255 #22 Feb 16 2025 08:33:28
%S A266255 1,4,3,124,3,2044,3,32764,3,524284,3,8388604,3,134217724,3,2147483644,
%T A266255 3,34359738364,3,549755813884,3,8796093022204,3,140737488355324,3,
%U A266255 2251799813685244,3,36028797018963964,3,576460752303423484,3,9223372036854775804,3
%N A266255 Decimal representation of the n-th iteration of the "Rule 11" elementary cellular automaton starting with a single ON (black) cell.
%C A266255 Rule 43 also generates this sequence.
%D A266255 S. Wolfram, A New Kind of Science, Wolfram Media, 2002; p. 55.
%H A266255 Robert Price, <a href="/A266255/b266255.txt">Table of n, a(n) for n = 0..999</a>
%H A266255 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/ElementaryCellularAutomaton.html">Elementary Cellular Automaton</a>
%H A266255 <a href="/index/Ce#cell">Index entries for sequences related to cellular automata</a>
%H A266255 <a href="https://oeis.org/wiki/Index_to_Elementary_Cellular_Automata">Index to Elementary Cellular Automata</a>
%F A266255 From _Colin Barker_, Dec 27 2015 and Apr 14 2019: (Start)
%F A266255 a(n) = (7*(-1)^n+2^(2*n+1)-(-1)^n*2^(2*n+1)-1)/2 for n>0.
%F A266255 a(n) = 17*a(n-2)-16*a(n-4) for n>4.
%F A266255 G.f.: (1+4*x-14*x^2+56*x^3-32*x^4) / ((1-x)*(1+x)*(1-4*x)*(1+4*x)).
%F A266255 (End)
%F A266255 a(n) = 2*4^n - 4 for odd n; a(n) = 3 - 2*0^n for even n. - _Karl V. Keller, Jr._, Aug 26 2021
%t A266255 rule=11; 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]],2],{k,1,rows}] (* Decimal Representation of Rows *)
%o A266255 (Python) print([2*4**n - 4 if n%2 else 3 - 2*0**n for n in range(33)]) # _Karl V. Keller, Jr._, Aug 26 2021
%Y A266255 Cf. A266253, A266254, A266070, A266071, A081253, A266256, A266257, A266258, A266259.
%K A266255 nonn,easy
%O A266255 0,2
%A A266255 _Robert Price_, Dec 25 2015