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A052822
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A simple grammar: pairs of cycles of cycles.
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1
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0, 0, 2, 12, 80, 630, 5816, 61978, 751222, 10225140, 154610048, 2573280820, 46775427860, 922374085984, 19616567407368, 447666534959528, 10913339500879576, 283081184691349600, 7785415448640271232
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,3
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LINKS
| INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 787
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FORMULA
| E.g.f.: ln(-1/(-1+ln(-1/(-1+x))))^2
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MAPLE
| pairs spec := [S, {B=Cycle(Z), C=Cycle(B), S=Prod(C, C)}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
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CROSSREFS
| Sequence in context: A082142 A069723 A063481 * A058872 A055548 A092850
Adjacent sequences: A052819 A052820 A052821 * A052823 A052824 A052825
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KEYWORD
| easy,nonn
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AUTHOR
| encyclopedia(AT)pommard.inria.fr, Jan 25 2000
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