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Search: id:A052838
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| 0, 0, 2, 18, 158, 1510, 15962, 186270, 2385182, 33290862, 503277242, 8193803926, 142938943886, 2659770747270, 52581058479770, 1100423513438766, 24302677755662654, 564770268904566238
(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 805
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FORMULA
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E.g.f.: (exp(-x/(-1+x))-1)^2
Recurrence: {a(1)=0, a(0)=0, a(2)=2, (4*n^3+2*n+5*n^2+n^4)*a(n)+(-4*n^3-35*n-18-21*n^2)*a(n+1)+(38+30*n+6*n^2)*a(n+2)+(-13-4*n)*a(n+3)+a(n+4), a(3)=18}
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MAPLE
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spec := [S, {C=Sequence(Z, 1 <= card), B=Set(C, 1 <= card), S=Prod(B, B)}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
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CROSSREFS
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Sequence in context: A125835 A091170 A091165 this_sequence A052876 A121933 A108550
Adjacent sequences: A052835 A052836 A052837 this_sequence A052839 A052840 A052841
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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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