A286772 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 221", based on the 5-celled von Neumann neighborhood.

1, 2, 0, 14, 1, 62, 1, 254, 1, 1022, 1, 4094, 1, 16382, 1, 65534, 1, 262142, 1, 1048574, 1, 4194302, 1, 16777214, 1, 67108862, 1, 268435454, 1, 1073741822, 1, 4294967294, 1, 17179869182, 1, 68719476734, 1, 274877906942, 1, 1099511627774, 1, 4398046511102, 1

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.

Links

Robert Price, Table of n, a(n) for n = 0..126

Robert Price, Diagrams of first 20 stages

N. J. A. Sloane, On the Number of ON Cells in Cellular Automata, arXiv:1503.01168 [math.CO], 2015

Eric Weisstein's World of Mathematics, Elementary Cellular Automaton

S. Wolfram, A New Kind of Science

Wolfram Research, Wolfram Atlas of Simple Programs

Index entries for sequences related to cellular automata

Index to 2D 5-Neighbor Cellular Automata

Index to Elementary Cellular Automata

Formula

Conjectures from Colin Barker, May 14 2017: (Start)

G.f.: (1 + 2*x - 5*x^2 + 4*x^3 + 5*x^4 - 4*x^6) / ((1 - x)*(1 + x)*(1 - 2*x)*(1 + 2*x)).

a(n) = 1 for n>2.

a(n) = 2^(n+1) - 2 for n>2.

a(n) = 5*a(n-2) - 4*a(n-4) for n>4.

(End)

It appears that a(n) = A280412(n) for n >= 3. - Michel Marcus, May 20 2017

Mathematica

CAStep[rule_, a_] := Map[rule[[10 - #]] &, ListConvolve[{{0, 2, 0}, {2, 1, 2}, {0, 2, 0}}, a, 2], {2}];
code = 221; 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

Cf. A286770, A286771, A286773.

Sequence in context: A286118 A286084 A286732 * A286505 A286405 A287131

Adjacent sequences: A286769 A286770 A286771 * A286773 A286774 A286775

Keyword

nonn,easy

Author

Robert Price, May 14 2017

Status

approved