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 A271005 Number of active (ON,black) cells at stage 2^n-1 of the two-dimensional cellular automaton defined by "Rule 245", based on the 5-celled von Neumann neighborhood. 0
 1, 8, 44, 208, 928, 3904, 16000, 64768, 260608, 1045504, 4188160, 16764928, 67084288, 268386304, 1073643520, 4294770688 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS Initialized with a single black (ON) cell at stage zero. It is conjectured that Rule 501 also produces this sequence.  It would be nice to have a proof. 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 FORMULA Conjecture: a(n) = 4*4^n - 6*2^n, n>2. - Lars Blomberg, Jun 08 2016 Conjectures from Colin Barker, Jun 08 2016: (Start) a(n) = 6*a(n-1)-8*a(n-2) for n>4. G.f.: (1+2*x+4*x^2+8*x^3+32*x^4) / ((1-2*x)*(1-4*x)). (End) MATHEMATICA CAStep[rule_, a_]:=Map[rule[[10-#]]&, ListConvolve[{{0, 2, 0}, {2, 1, 2}, {0, 2, 0}}, a, 2], {2}]; code=245; 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. A271004. Sequence in context: A003518 A100575 A272112 * A003220 A270318 A270330 Adjacent sequences:  A271002 A271003 A271004 * A271006 A271007 A271008 KEYWORD nonn,more AUTHOR Robert Price, Mar 28 2016 EXTENSIONS a(8)-a(15) from Lars Blomberg, Jun 08 2016 STATUS approved

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Last modified November 15 15:59 EST 2018. Contains 317239 sequences. (Running on oeis4.)