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A052719
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A simple context-free grammar in a labeled universe.
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0
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0, 0, 0, 6, 72, 1080, 20160, 453600, 11975040, 363242880, 12454041600, 476367091200, 20113277184000, 929233405900800, 46630621823385600, 2525825348766720000, 146886458743664640000, 9127944221927731200000
(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 675
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FORMULA
| E.g.f.: (1/2-x-1/2*(1-4*x)^(1/2))*(1/2-1/2*(1-4*x)^(1/2))
Recurrence: {a(1)=0, a(2)=0, a(3)=6, (-2*n-6+4*n^2)*a(n)+(-2-5*n)*a(n+1)+a(n+2)}
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MAPLE
| spec := [S, {B=Union(Z, C), C=Prod(B, B), S=Prod(B, C)}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
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CROSSREFS
| Sequence in context: A113331 A156128 A052678 * A196882 A063965 A047058
Adjacent sequences: A052716 A052717 A052718 * A052720 A052721 A052722
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KEYWORD
| easy,nonn
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AUTHOR
| encyclopedia(AT)pommard.inria.fr, Jan 25 2000
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