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A052876
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A simple grammar.
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1
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0, 0, 2, 18, 158, 1530, 16622, 201978, 2724878, 40492890, 657944942, 11611834938, 221291822798, 4530383962650, 99179581033262, 2312402554523898, 57211901491595918, 1497211181084718810
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,3
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COMMENTS
| a(n)=A069321(n)-A000670(n). - Mario Catalani (mario.catalani(AT)unito.it), Dec 22 2003
a(n)=2*A091106(n)+2 - Mario Catalani (mario.catalani(AT)unito.it), Dec 22 2003
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LINKS
| INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 847
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FORMULA
| E.g.f.: (exp(x)-1)^2/(-2+exp(x))^2
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MAPLE
| spec := [S, {B=Set(Z, 1 <= card), C=Sequence(B, 1 <= card), S=Prod(C, C)}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
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CROSSREFS
| Sequence in context: A091165 A191814 A052838 * A121933 A108550 A144513
Adjacent sequences: A052873 A052874 A052875 * A052877 A052878 A052879
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KEYWORD
| easy,nonn
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AUTHOR
| encyclopedia(AT)pommard.inria.fr, Jan 25 2000
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