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A290828
Decimal representation of the diagonal from the corner to the origin of the n-th stage of growth of the two-dimensional cellular automaton defined by "Rule 961", based on the 5-celled von Neumann neighborhood.
4
1, 2, 5, 15, 28, 63, 124, 255, 508, 1023, 2044, 4095, 8188, 16383, 32764, 65535, 131068, 262143, 524284, 1048575, 2097148, 4194303, 8388604, 16777215, 33554428, 67108863, 134217724, 268435455, 536870908, 1073741823, 2147483644, 4294967295, 8589934588
OFFSET
0,2
COMMENTS
Initialized with a single black (ON) cell at stage zero.
REFERENCES
S. Wolfram, A New Kind of Science, Wolfram Media, 2002; p. 170.
FORMULA
Conjectures from Colin Barker, Aug 12 2017: (Start)
G.f.: (1 + 5*x^3 - 3*x^4 + 2*x^5) / ((1 - x)*(1 + x)*(1 - 2*x)).
a(n) = 2*(2^n - 2) for n>2 and even.
a(n) = 2^(n+1) - 1 for n>2 and odd.
a(n) = 2*a(n-1) + a(n-2) - 2*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 = 961; 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
KEYWORD
nonn,easy
AUTHOR
Robert Price, Aug 11 2017
STATUS
approved