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A290234
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 773", based on the 5-celled von Neumann neighborhood.
4
1, 2, 7, 12, 31, 56, 127, 240, 511, 992, 2047, 4032, 8191, 16256, 32767, 65280, 131071, 261632, 524287, 1047552, 2097151, 4192256, 8388607, 16773120, 33554431, 67100672, 134217727, 268419072, 536870911, 1073709056, 2147483647, 4294901760, 8589934591
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, Jul 25 2017: (Start)
G.f.: (1-2*x^3) / ((1-x)*(1+x)*(1-2*x)*(1-2*x^2)).
a(n) = 2^(n+1) - 1 for n even.
a(n) = 2^(n+1) - 2^((n+1)/2) for n odd.
a(n) = 2*a(n-1) + 3*a(n-2) - 6*a(n-3) - 2*a(n-4) + 4*a(n-5) for n>4.
(End)
MATHEMATICA
CAStep[rule_, a_] := Map[rule[[10 - #]] &, ListConvolve[{{0, 2, 0}, {2, 1, 2}, {0, 2, 0}}, a, 2], {2}];
code = 773; 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, Jul 24 2017
STATUS
approved