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A052700
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E.g.f. x*(1-x)/(1-3x).
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0
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0, 1, 4, 36, 432, 6480, 116640, 2449440, 58786560, 1587237120, 47617113600, 1571364748800, 56569130956800, 2206196107315200, 92660236507238400, 4169710642825728000, 200146110855634944000, 10207451653637382144000
(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 650
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FORMULA
| E.g.f.: x*(-1+x)/(-1+3*x)
Recurrence: {a(1)=1, a(0)=0, a(2)=4, (-3*n-3)*a(n)+a(n+1)=0}
2/9*3^n*n!, n>1.
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MAPLE
| spec := [S, {S=Prod(Z, Sequence(Prod(Sequence(Z), Union(Z, Z))))}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
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CROSSREFS
| Sequence in context: A202828 A131765 A132864 * A167540 A136224 A009533
Adjacent sequences: A052697 A052698 A052699 * A052701 A052702 A052703
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KEYWORD
| easy,nonn
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AUTHOR
| encyclopedia(AT)pommard.inria.fr, Jan 25 2000
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