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A052744
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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, 48, 840, 17280, 448560, 13789440, 491702400, 19929369600, 904873939200, 45486949939200, 2507639957222400, 150419515915468800, 9752720435377920000, 679630757528346624000, 50655177765863903232000
(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 700
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FORMULA
| E.g.f.: (1/2)/(x^2+1+2*x)*(1-2*x-2*x^2-(1-4*x-4*x^2)^(1/2))*x
Recurrence: {a(1)=0, a(2)=0, a(3)=6, (-4*n^4-24*n-24*n^3-44*n^2)*a(n)+(-8*n^3-42*n^2-12-58*n)*a(n+1)+(-3*n^2-8*n+3)*a(n+2)+(n+2)*a(n+3), a(4)=48, a(5)=840, a(6)=17280}
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MAPLE
| spec := [S, {B=Prod(C, C), S=Prod(B, Z), C=Union(B, S, Z)}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
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CROSSREFS
| Sequence in context: A113393 A138426 A108092 * A192769 A084259 A028308
Adjacent sequences: A052741 A052742 A052743 * A052745 A052746 A052747
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KEYWORD
| easy,nonn
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AUTHOR
| encyclopedia(AT)pommard.inria.fr, Jan 25 2000
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