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A271132
First differences of number of active (ON, black) cells in n-th stage of growth of two-dimensional cellular automaton defined by "Rule 291", based on the 5-celled von Neumann neighborhood.
1
4, 4, 23, -23, 92, -60, 123, -131, 283, -255, 372, -380, 547, -459, 684, -749, 1021, -937, 1125, -1193, 1537, -1361, 1541, -1536, 2052, -2073, 2337, -2325, 2625, -2468, 2928, -2953, 3413, -3369, 3769, -3816, 4400, -4128, 4459, -4571, 5439, -5343, 5672, -5692
OFFSET
0,1
COMMENTS
Initialized with a single black (ON) cell at stage zero.
REFERENCES
S. Wolfram, A New Kind of Science, Wolfram Media, 2002; p. 170.
MATHEMATICA
CAStep[rule_, a_]:=Map[rule[[10-#]]&, ListConvolve[{{0, 2, 0}, {2, 1, 2}, {0, 2, 0}}, a, 2], {2}];
code=291; 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[on[[i+1]]-on[[i]], {i, 1, Length[on]-1}] (* Difference at each stage *)
CROSSREFS
Cf. A271129.
Sequence in context: A271249 A271167 A271155 * A270456 A088304 A131978
KEYWORD
sign,easy
AUTHOR
Robert Price, Mar 31 2016
STATUS
approved