OFFSET
0,2
COMMENTS
Initialized with a single black (ON) cell at stage zero.
It is conjectured that Rule 501 also produces this sequence. It would be nice to have a proof.
REFERENCES
S. Wolfram, A New Kind of Science, Wolfram Media, 2002; p. 170.
LINKS
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
FORMULA
Conjecture: a(n) = 4*4^n - 6*2^n, n>2. - Lars Blomberg, Jun 08 2016
Conjectures from Colin Barker, Jun 08 2016: (Start)
a(n) = 6*a(n-1)-8*a(n-2) for n>4.
G.f.: (1+2*x+4*x^2+8*x^3+32*x^4) / ((1-2*x)*(1-4*x)).
(End)
MATHEMATICA
CAStep[rule_, a_]:=Map[rule[[10-#]]&, ListConvolve[{{0, 2, 0}, {2, 1, 2}, {0, 2, 0}}, a, 2], {2}];
code=245; 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 *)
Part[on, 2^Range[0, Log[2, stages]]] (* Extract relevant terms *)
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Robert Price, Mar 28 2016
EXTENSIONS
a(8)-a(15) from Lars Blomberg, Jun 08 2016
STATUS
approved