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 A283356 Binary representation of the x-axis, from the origin to the right edge, of the n-th stage of growth of the two-dimensional cellular automaton defined by "Rule 621", based on the 5-celled von Neumann neighborhood. 4
 1, 1, 1, 1101, 10001, 11101, 110001, 1111101, 11110001, 111111101, 1111110001, 11111111101, 111111110001, 1111111111101, 11111111110001, 111111111111101, 1111111111110001, 11111111111111101, 111111111111110001, 1111111111111111101, 11111111111111110001 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,4 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, Mar 06 2017: (Start) G.f.: (1 - 9*x - 10*x^2 + 1100*x^3 - 1000*x^4 - 90000*x^5 + 100000*x^7) / ((1 - x)*(1 + x)*(1 - 10*x)). a(n) = (10^n - 9991) / 9 for n>4 and even. a(n) = (10^n - 91) / 9 for n>4 and odd. a(n) = 10*a(n-1) + a(n-2) - 10*a(n-3) for n>5. (End) MATHEMATICA CAStep[rule_, a_] := Map[rule[[10 - #]] &, ListConvolve[{{0, 2, 0}, {2, 1, 2}, {0, 2, 0}}, a, 2], {2}]; code = 621; 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[i, 2 * i - 1]], 10], {i, 1, stages - 1}] CROSSREFS Cf. A283355, A283357, A283358. Sequence in context: A283215 A283388 A283405 * A283172 A283253 A178407 Adjacent sequences:  A283353 A283354 A283355 * A283357 A283358 A283359 KEYWORD nonn,easy AUTHOR Robert Price, Mar 05 2017 STATUS approved

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Last modified December 14 09:41 EST 2019. Contains 329979 sequences. (Running on oeis4.)