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A052867
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A simple grammar.
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0
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0, 0, 2, 12, 84, 720, 7440, 90720, 1280160, 20563200, 370863360, 7424524800, 163419379200, 3923023104000, 102011054745600, 2856483889459200, 85697132032512000, 2742350070620160000, 93240613775941632000
(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 838
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FORMULA
| E.g.f.: ln(-(-1+x)^2/(-1+2*x))
Recurrence: {a(1)=0, a(2)=2, (2*n^2+2*n)*a(n)-3*(n+1)*a(n+1)+a(n+2)}
-2*GAMMA(n+1)+2^(n+1)*GAMMA(n+1)
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MAPLE
| spec := [S, {B=Sequence(Z, 1 <= card), C=Prod(B, B), S= Cycle(C)}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
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CROSSREFS
| Sequence in context: A006657 A105927 A052887 * A179495 A097237 A055531
Adjacent sequences: A052864 A052865 A052866 * A052868 A052869 A052870
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KEYWORD
| easy,nonn
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AUTHOR
| encyclopedia(AT)pommard.inria.fr, Jan 25 2000
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