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Search: id:A052721
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| A052721 |
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A simple context-free grammar in a labeled universe. |
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+0
1
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| 0, 0, 0, 0, 0, 120, 2880, 70560, 1935360, 59875200, 2075673600, 79913433600, 3387499315200, 156883562035200, 7884404656128000, 427447366714368000, 24869664972472320000, 1545805113445232640000, 102232975285590589440000
(list; graph; listen)
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OFFSET
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0,6
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LINKS
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INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 677
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FORMULA
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E.g.f.: -(-1/2+x+1/2*(1-4*x)^(1/2)+2*(1/2-x-1/2*(1-4*x)^(1/2))*x+x^2)*x
Recurrence: {a(1)=0, a(2)=0, a(4)=0, a(3)=0, (4*n^2-44*n+8*n^3-40)*a(n)+(-8*n-6*n^2+8)*a(n+1)+(n+1)*a(n+2), a(5)=120, a(6)=2880}
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MAPLE
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spec := [S, {C=Union(B, Z), B=Prod(C, C), S=Prod(B, B, Z)}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
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CROSSREFS
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Sequence in context: A000553 A126232 A105943 this_sequence A060490 A052722 A139389
Adjacent sequences: A052718 A052719 A052720 this_sequence A052722 A052723 A052724
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KEYWORD
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easy,nonn
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AUTHOR
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encyclopedia(AT)pommard.inria.fr, Jan 25 2000
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