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A266794
Number of OFF (white) cells in the n-th iteration of the "Rule 61" elementary cellular automaton starting with a single ON (black) cell.
2
0, 1, 3, 2, 5, 4, 8, 4, 12, 4, 16, 4, 20, 4, 24, 4, 28, 4, 32, 4, 36, 4, 40, 4, 44, 4, 48, 4, 52, 4, 56, 4, 60, 4, 64, 4, 68, 4, 72, 4, 76, 4, 80, 4, 84, 4, 88, 4, 92, 4, 96, 4, 100, 4, 104, 4, 108, 4, 112, 4, 116, 4, 120, 4, 124, 4, 128, 4, 132, 4, 136, 4
OFFSET
0,3
REFERENCES
S. Wolfram, A New Kind of Science, Wolfram Media, 2002; p. 55.
FORMULA
Conjectures from Colin Barker, Jan 04 2016 and Apr 17 2019: (Start)
a(n) = n+(-1)^n*(n-4) for n>4.
a(n) = 2*a(n-2)-a(n-4) for n>7.
G.f.: x*(1+3*x-x^3+x^4+x^5-2*x^6+x^7) / ((1-x)^2*(1+x)^2).
(End)
MATHEMATICA
rule=61; 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. A266786.
Cf. A266795 (partial sums).
Sequence in context: A164380 A143527 A284153 * A340286 A194078 A169752
KEYWORD
nonn,easy
AUTHOR
Robert Price, Jan 03 2016
STATUS
approved