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 A282798 Decimal representation of the x-axis, from the left edge to the origin, of the n-th stage of growth of the two-dimensional cellular automaton defined by "Rule 505", based on the 5-celled von Neumann neighborhood. 4
 1, 0, 7, 4, 31, 20, 127, 84, 511, 340, 2047, 1364, 8191, 5460, 32767, 21844, 131071, 87380, 524287, 349524, 2097151, 1398100, 8388607, 5592404, 33554431, 22369620, 134217727, 89478484, 536870911, 357913940, 2147483647, 1431655764, 8589934591, 5726623060 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS Initialized with a single black (ON) cell at stage zero. REFERENCES S. Wolfram, A New Kind of Science, Wolfram Media, 2002; p. 170. LINKS Robert Price, Table of n, a(n) for n = 0..126 Robert Price, Diagrams of first 20 stages 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 Wolfram Research, Wolfram Atlas of Simple Programs FORMULA Conjectures from Colin Barker, Feb 21 2017: (Start) a(n) = 2^(n+1) - 1 for n even. a(n) = 2*(2^n-2) / 3 for n odd. a(n) = 5*a(n-2) - 4*a(n-4) for n>3. G.f.: (1 + 2*x^2 + 4*x^3) / ((1 - x)*(1 + x)*(1 - 2*x)*(1 + 2*x)). (End) MATHEMATICA CAStep[rule_, a_] := Map[rule[[10 - #]] &, ListConvolve[{{0, 2, 0}, {2, 1, 2}, {0, 2, 0}}, a, 2], {2}]; code = 505; 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}]; Table[FromDigits[Part[ca[[i]] [[i]], Range[1, i]], 2], {i, 1, stages - 1}] CROSSREFS Cf. A282796, A282797, A282799. Sequence in context: A282259 A282453 A282654 * A282802 A248278 A270235 Adjacent sequences:  A282795 A282796 A282797 * A282799 A282800 A282801 KEYWORD nonn,easy AUTHOR Robert Price, Feb 21 2017 STATUS approved

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Last modified December 8 14:38 EST 2019. Contains 329865 sequences. (Running on oeis4.)