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A277800
Decimal representation of the x-axis, from the origin to the right edge, of the n-th stage of growth of the two-dimensional cellular automaton defined by "Rule 1", based on the 5-celled von Neumann neighborhood.
5
1, 0, 4, 3, 16, 15, 64, 63, 256, 255, 1024, 1023, 4096, 4095, 16384, 16383, 65536, 65535, 262144, 262143, 1048576, 1048575, 4194304, 4194303, 16777216, 16777215, 67108864, 67108863, 268435456, 268435455, 1073741824, 1073741823, 4294967296, 4294967295
OFFSET
0,3
COMMENTS
Initialized with a single black (ON) cell at stage zero.
Rule numbers 1, 9, 17, 25, 257, 265, 273 and 281 all generate this sequence.
REFERENCES
S. Wolfram, A New Kind of Science, Wolfram Media, 2002; p. 170.
FORMULA
Conjectures from Colin Barker, Nov 01 2016: (Start)
G.f.: (1 - x^2 + 3*x^3)/((1 - x)*(1 + x)*(1 - 2*x)*(1 + 2*x)).
a(n) = 5*a(n-2) - 4*a(n-4) for n>3.
a(n) = (-2+(-2)^n+2*(-1)^n+3*2^n)/4. (End)
MATHEMATICA
CAStep[rule_, a_]:=Map[rule[[10-#]]&, ListConvolve[{{0, 2, 0}, {2, 1, 2}, {0, 2, 0}}, a, 2], {2}];
code=1; 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]], 2], {i, 1, stages-1}]
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Robert Price, Oct 31 2016
STATUS
approved