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Search: id:A052887
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| 1, 0, 2, 12, 84, 720, 7320, 85680, 1130640, 16571520, 266747040, 4673592000, 88476252480, 1798674958080, 39061703640960, 902110060051200, 22068313153286400, 569874634276147200, 15486794507222438400
(list; graph; listen)
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OFFSET
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0,3
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LINKS
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INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 860
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FORMULA
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E.g.f.: exp(x^2/(-1+x)^2)
Recurrence: {a(1)=0, a(0)=1, a(2)=2, (-n^3-2*n-3*n^2)*a(n)+(3*n^2+7*n+2)*a(n+1)+(-6-3*n)*a(n+2)+a(n+3)}
Sum_{k=0..floor(n/2)} n!/k!*binomial(n-1, 2*k-1). - Vladeta Jovovic (vladeta(AT)eunet.rs), Sep 13 2003
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MAPLE
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spec := [S, {B=Sequence(Z, 1 <= card), C=Prod(B, B), S= Set(C)}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
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CROSSREFS
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Sequence in context: A130464 A006657 A105927 this_sequence A052867 A097237 A055531
Adjacent sequences: A052884 A052885 A052886 this_sequence A052888 A052889 A052890
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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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