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 A267851 #23 Jun 24 2025 12:37:59
%S A267851 1,2,30,126,510,2046,8190,32766,131070,524286,2097150,8388606,
%T A267851 33554430,134217726,536870910,2147483646,8589934590,34359738366,
%U A267851 137438953470,549755813886,2199023255550,8796093022206,35184372088830,140737488355326,562949953421310
%N A267851 Decimal representation of the n-th iteration of the "Rule 229" elementary cellular automaton starting with a single ON (black) cell.
%D A267851 S. Wolfram, A New Kind of Science, Wolfram Media, 2002; p. 55.
%H A267851 Robert Price, <a href="/A267851/b267851.txt">Table of n, a(n) for n = 0..1000</a>
%H A267851 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/ElementaryCellularAutomaton.html">Elementary Cellular Automaton</a>
%H A267851 S. Wolfram, <a href="http://wolframscience.com/">A New Kind of Science</a>
%H A267851 <a href="/index/Ce#cell">Index entries for sequences related to cellular automata</a>
%H A267851 <a href="https://oeis.org/wiki/Index_to_Elementary_Cellular_Automata">Index to Elementary Cellular Automata</a>
%F A267851 Conjectures from _Colin Barker_, Jan 21 2016: (Start)
%F A267851 a(n) = 5*a(n-1)-4*a(n-2) for n>3.
%F A267851 G.f.: (1-3*x+24*x^2-16*x^3) / ((1-x)*(1-4*x)).
%F A267851 (End)
%F A267851 Conjecture: a(n) = 2*(4^n - 1) = A002446(n) for n>1. - _Colin Barker_, Nov 26 2016
%t A267851 rule=229; 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 *)
%Y A267851 Cf. A267848.
%K A267851 nonn
%O A267851 0,2
%A A267851 _Robert Price_, Jan 21 2016