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A273311
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Partial sums of the number of active (ON,black) cells in n-th stage of growth of two-dimensional cellular automaton defined by "Rule 641", based on the 5-celled von Neumann neighborhood.
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1
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1, 5, 22, 62, 135, 247, 408, 624, 905, 1257, 1690, 2210, 2827, 3547, 4380, 5332, 6413, 7629, 8990, 10502, 12175, 14015, 16032, 18232, 20625, 23217, 26018, 29034, 32275, 35747, 39460, 43420, 47637, 52117, 56870, 61902, 67223, 72839, 78760, 84992, 91545, 98425
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OFFSET
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0,2
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COMMENTS
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Initialized with a single black (ON) cell at stage zero.
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REFERENCES
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S. Wolfram, A New Kind of Science, Wolfram Media, 2002; p. 170.
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LINKS
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FORMULA
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a(n) = (57+3*(-1)^n-58*n+48*n^2+16*n^3)/12 for n>0.
a(n) = (8*n^3+24*n^2-29*n+30)/6 for n>0 and even.
a(n) = (8*n^3+24*n^2-29*n+27)/6 for n>0 and odd.
a(n) = 3*a(n-1)-2*a(n-2)-2*a(n-3)+3*a(n-4)-a(n-5) for n>5.
G.f.: (1+2*x+9*x^2+8*x^3-4*x^5) / ((1-x)^4*(1+x)).
(End)
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MATHEMATICA
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CAStep[rule_, a_]:=Map[rule[[10-#]]&, ListConvolve[{{0, 2, 0}, {2, 1, 2}, {0, 2, 0}}, a, 2], {2}];
code=641; 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}];
on=Map[Function[Apply[Plus, Flatten[#1]]], ca] (* Count ON cells at each stage *)
Table[Total[Part[on, Range[1, i]]], {i, 1, Length[on]}] (* Sum at each stage *)
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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