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Search: id:A052631
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| 0, 1, 4, 30, 288, 3480, 50400, 851760, 16450560, 357436800, 8629286400, 229162348800, 6638962176000, 208362342988800, 7042436719718400, 255029193619200000, 9851119008546816000, 404305986955014144000, 17569457946995834880000, 805912049524456562688000
(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 577
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FORMULA
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E.g.f.: -x/(-1+2*x+x^2)
Recurrence: {a(1)=1, a(0)=0, (-2-n^2-3*n)*a(n)+(-4-2*n)*a(n+1)+a(n+2)}
Sum(-1/4*(-1+_alpha)*_alpha^(-1-n), _alpha=RootOf(-1+2*_Z+_Z^2))*n!
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MAPLE
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spec := [S, {S=Prod(Z, Sequence(Union(Z, Z, Prod(Z, Z))))}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
with(combstruct):ZL:=[T, {T=Union(Z, Prod(Epsilon, Z, T), Prod(T, Z, Epsilon), Prod(T, Z, Z))}, labeled]:seq(count(ZL, size=i), i=0..19); - Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), Dec 16 2007
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CROSSREFS
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Sequence in context: A102307 A052658 A127130 this_sequence A167139 A054972 A052452
Adjacent sequences: A052628 A052629 A052630 this_sequence A052632 A052633 A052634
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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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