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A052833
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A simple grammar.
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0
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0, 0, 2, 12, 72, 500, 4080, 38668, 419160, 5124708, 69831360, 1049972924, 17273719848, 308714206996, 5956836347280, 123437573728620, 2734197673727736, 64473939310567364, 1612626113517932640
(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 799
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FORMULA
| E.g.f.: ln(-1/(-2+exp(x)))^2
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MAPLE
| spec := [S, {B=Set(Z, 1 <= card), 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: A018931 A062119 A052556 * A144086 A005443 A002867
Adjacent sequences: A052830 A052831 A052832 * A052834 A052835 A052836
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KEYWORD
| easy,nonn
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AUTHOR
| encyclopedia(AT)pommard.inria.fr, Jan 25 2000
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