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A052823
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A simple grammar: cycles of pairs of sequences.
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6
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0, 0, 1, 2, 4, 6, 12, 18, 34, 58, 106, 186, 350, 630, 1180, 2190, 4114, 7710, 14600, 27594, 52486
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OFFSET
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0,4
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LINKS
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Table of n, a(n) for n=0..20.
INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 788
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FORMULA
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G.f.: Sum(numtheory[phi](j[1])/j[1]*ln(-(x^j[1]-1)^2/(2*x^j[1]-1)), j[1]=1 .. infinity)
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MAPLE
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spec := [S, {B=Sequence(Z, 1 <= card), C=Prod(B, B), S= Cycle(C)}, unlabeled]: seq(combstruct[count](spec, size=n), n=0..20);
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CROSSREFS
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A000031 - 2.
Sequence in context: A167777 A007436 A052847 * A063516 A104352 A133488
Adjacent sequences: A052820 A052821 A052822 * A052824 A052825 A052826
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KEYWORD
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easy,nonn
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AUTHOR
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encyclopedia(AT)pommard.inria.fr, Jan 25 2000
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STATUS
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approved
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