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A282413
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 467", based on the 5-celled von Neumann neighborhood.
4
1, 1, 7, 0, 31, 0, 127, 0, 511, 0, 2047, 0, 8191, 0, 32767, 0, 131071, 0, 524287, 0, 2097151, 0, 8388607, 0, 33554431, 0, 134217727, 0, 536870911, 0, 2147483647, 0, 8589934591, 0, 34359738367, 0, 137438953471, 0, 549755813887, 0, 2199023255551, 0
OFFSET
0,3
COMMENTS
Initialized with a single black (ON) cell at stage zero.
For n != 1, is a(n) = A279872(n)? - Bruno Berselli, Feb 15 2017
REFERENCES
S. Wolfram, A New Kind of Science, Wolfram Media, 2002; p. 170.
FORMULA
Conjectures from Colin Barker, Feb 15 2017: (Start)
a(n) = 2^(n+1)-1 for n>1 and even.
a(n) = 0 for n>1 and odd.
a(n) = 5*a(n-2) - 4*a(n-4) for n>3.
G.f.: (1 + x + 2*x^2 - 5*x^3 + 4*x^5) / ((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 = 467; 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
KEYWORD
nonn,easy
AUTHOR
Robert Price, Feb 14 2017
STATUS
approved