login

Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).

A273827
Number of active (ON, black) cells in n-th stage of growth of two-dimensional cellular automaton defined by "Rule 950", based on the 5-celled von Neumann neighborhood.
4
1, 5, 9, 25, 37, 53, 65, 109, 141, 173, 201, 253, 293, 341, 369, 477, 541, 605, 665, 749, 821, 901, 961, 1093, 1181, 1277, 1353, 1485, 1573, 1685, 1745, 1981, 2109, 2237, 2361, 2509, 2645, 2789, 2913, 3109, 3261, 3421, 3561, 3757, 3909, 4085, 4209, 4501
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.
MATHEMATICA
CAStep[rule_, a_]:=Map[rule[[10-#]]&, ListConvolve[{{0, 2, 0}, {2, 1, 2}, {0, 2, 0}}, a, 2], {2}];
code=950; 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}];
Map[Function[Apply[Plus, Flatten[#1]]], ca] (* Count ON cells at each stage *)
CROSSREFS
Sequence in context: A234277 A269918 A354775 * A024825 A147074 A147192
KEYWORD
nonn,easy
AUTHOR
Robert Price, May 31 2016
STATUS
approved