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A266258
Number of OFF (white) cells in the n-th iteration of the "Rule 11" elementary cellular automaton starting with a single ON (black) cell.
3
0, 2, 3, 2, 7, 2, 11, 2, 15, 2, 19, 2, 23, 2, 27, 2, 31, 2, 35, 2, 39, 2, 43, 2, 47, 2, 51, 2, 55, 2, 59, 2, 63, 2, 67, 2, 71, 2, 75, 2, 79, 2, 83, 2, 87, 2, 91, 2, 95, 2, 99, 2, 103, 2, 107, 2, 111, 2, 115, 2, 119, 2, 123, 2, 127, 2, 131, 2, 135, 2, 139, 2
OFFSET
0,2
REFERENCES
S. Wolfram, A New Kind of Science, Wolfram Media, 2002; p. 55.
FORMULA
Conjectures from Colin Barker, Dec 27 2015 and Apr 14 2019: (Start)
a(n) = (2*(-1)^n*n+2*n-3*(-1)^n+1)/2 for n>0
a(n) = 2*a(n-2)-a(n-4) for n>4.
G.f.: x*(2+3*x-2*x^2+x^3) / ((1-x)^2*(1+x)^2).
(End)
MATHEMATICA
rule=11; rows=20; ca=CellularAutomaton[rule, {{1}, 0}, rows-1, {All, All}]; (* Start with single black cell *) catri=Table[Take[ca[[k]], {rows-k+1, rows+k-1}], {k, 1, rows}]; (* Truncated list of each row *) nbc=Table[Total[catri[[k]]], {k, 1, rows}]; (* Number of Black cells in stage n *) Table[Length[catri[[k]]]-nbc[[k]], {k, 1, rows}] (* Number of White cells in stage n *)
CROSSREFS
Cf. A266253.
Sequence in context: A262427 A333986 A349664 * A354486 A180916 A319374
KEYWORD
nonn,easy
AUTHOR
Robert Price, Dec 25 2015
EXTENSIONS
Conjectures from Colin Barker, Apr 14 2019
STATUS
approved