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A052821
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A simple grammar: pairs of cycles of sequences.
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0
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0, 0, 1, 4, 10, 22, 43, 84, 157, 294, 551, 1032, 1941, 3666, 6955, 13224, 25269, 48362, 92875, 178640, 344453
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,4
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LINKS
| INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 786
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FORMULA
| G.f.: Sum(numtheory[phi](j[1])/j[1]*ln((x^j[1]-1)/(2*x^j[1]-1)), j[1]=1 .. infinity)^2
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MAPLE
| pairs spec := [S, {B=Sequence(Z, 1 <= card), C=Cycle(B), S=Prod(C, C)}, unlabeled]: seq(combstruct[count](spec, size=n), n=0..20);
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CROSSREFS
| Sequence in context: A023626 A048574 A052837 * A023628 A004798 A174622
Adjacent sequences: A052818 A052819 A052820 * A052822 A052823 A052824
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KEYWORD
| easy,nonn
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AUTHOR
| encyclopedia(AT)pommard.inria.fr, Jan 25 2000
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