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A052690
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E.g.f. x*(1+x-3x^2)/(1-3x).
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0
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0, 1, 8, 54, 648, 9720, 174960, 3674160, 88179840, 2380855680, 71425670400, 2357047123200, 84853696435200, 3309294160972800, 138990354760857600, 6254565964238592000, 300219166283452416000, 15311177480456073216000
(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 638
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FORMULA
| E.g.f.: x*(-x+3*x^2-1)/(-1+3*x)
Recurrence: {a(1)=1, a(0)=0, a(2)=8, (-3*n-3)*a(n)+a(n+1)=0, a(3)=54}
3^(n-1)*n!, n>2.
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MAPLE
| spec := [S, {S=Prod(Z, Union(Z, Sequence(Union(Z, Z, Z))))}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
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CROSSREFS
| Sequence in context: A138403 A013499 A134825 * A027525 A080312 A116885
Adjacent sequences: A052687 A052688 A052689 * A052691 A052692 A052693
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KEYWORD
| easy,nonn
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AUTHOR
| encyclopedia(AT)pommard.inria.fr, Jan 25 2000
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