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A052586
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E.g.f. (1-x^3)/(1-x-x^3).
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0
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1, 1, 2, 6, 48, 360, 2880, 30240, 362880, 4717440, 68947200, 1117670400, 19639065600, 373621248000, 7671689625600, 168689993472000, 3954407288832000, 98525417582592000, 2599363724525568000
(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 531
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FORMULA
| E.g.f.: (-1+x^3)/(-1+x+x^3)
Recurrence: {a(1)=1, a(0)=1, a(3)=6, a(2)=2, (-11*n-6-n^3-6*n^2)*a(n) +(-n-3)*a(n+2) +a(n+3)=0}
Sum(1/31*(-2*_alpha+9*_alpha^2+6)*_alpha^(-1-n), _alpha=RootOf(-1+_Z+_Z^3))*n!
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MAPLE
| spec := [S, {S=Sequence(Prod(Z, Sequence(Prod(Z, Z, Z))))}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
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CROSSREFS
| Sequence in context: A052657 A092143 A052593 * A052554 A195203 A052743
Adjacent sequences: A052583 A052584 A052585 * A052587 A052588 A052589
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KEYWORD
| easy,nonn
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AUTHOR
| encyclopedia(AT)pommard.inria.fr, Jan 25 2000
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