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 A273708 Number of active (ON,black) cells at stage 2^n-1 of the two-dimensional cellular automaton defined by "Rule 873", based on the 5-celled von Neumann neighborhood. 0
 1, 4, 33, 193, 817, 3553, 14385, 58393, 236281, 947729, 3798161, 15196761, 60836513, 243349417, 973538641, 3894415281 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS Initialized with a single black (ON) cell at stage zero. Conjecture: Rule 889 also generates this sequence. - Lars Blomberg, Jul 24 2016 REFERENCES S. Wolfram, A New Kind of Science, Wolfram Media, 2002; p. 170. LINKS N. J. A. Sloane, On the Number of ON Cells in Cellular Automata, arXiv:1503.01168 [math.CO], 2015 Eric Weisstein's World of Mathematics, Elementary Cellular Automaton S. Wolfram, A New Kind of Science MATHEMATICA CAStep[rule_, a_]:=Map[rule[[10-#]]&, ListConvolve[{{0, 2, 0}, {2, 1, 2}, {0, 2, 0}}, a, 2], {2}]; code=873; stages=128; rule=IntegerDigits[code, 2, 10]; g=2*stages+1; (* Maximum size of grid *) a=PadLeft[{{1}}, {g, g}, 0, Floor[{g, g}/2]]; (* Initial ON cell on grid *) ca=a; ca=Table[ca=CAStep[rule, ca], {n, 1, stages+1}]; PrependTo[ca, a]; (* Trim full grid to reflect growth by one cell at each stage *) k=(Length[ca[[1]]]+1)/2; ca=Table[Table[Part[ca[[n]][[j]], Range[k+1-n, k-1+n]], {j, k+1-n, k-1+n}], {n, 1, k}]; on=Map[Function[Apply[Plus, Flatten[#1]]], ca] (* Count ON cells at each stage *) Part[on, 2^Range[0, Log[2, stages]]] (* Extract relevant terms *) CROSSREFS Cf. A273707. Sequence in context: A273676 A013192 A273700 * A097705 A131509 A221030 Adjacent sequences:  A273705 A273706 A273707 * A273709 A273710 A273711 KEYWORD nonn,more AUTHOR Robert Price, May 28 2016 EXTENSIONS a(8)-a(15) from Lars Blomberg, Jul 24 2016 STATUS approved

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Last modified January 26 11:45 EST 2022. Contains 350598 sequences. (Running on oeis4.)