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A052559
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E.g.f. (1-x)/(1-2x-x^2+x^3).
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0
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1, 1, 6, 36, 336, 3720, 50400, 791280, 14232960, 287763840, 6466521600, 159826867200, 4309577395200, 125885452492800, 3960073877760000, 133473015067392000, 4798579092443136000, 183299247820136448000
(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 501
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FORMULA
| E.g.f.: -(-1+x)/(x^3-x^2-2*x+1)
Recurrence: {a(1)=1, a(0)=1, a(2)=6, (n^3+6*n^2+11*n+6)*a(n) +(-n^2-5*n-6)*a(n+1) +(-2*n-6)*a(n+2) +a(n+3)=0}
Sum(-1/7*(-2*_alpha+_alpha^2-1)*_alpha^(-1-n), _alpha=RootOf(_Z^3-_Z^2-2*_Z+1))*n!
a(n) = n!*A077998(n). - R. J. Mathar, Nov 27 2011
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MAPLE
| spec := [S, {S=Sequence(Prod(Z, Union(Z, Sequence(Z))))}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
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CROSSREFS
| Sequence in context: A047898 A098559 A129584 * A053335 A108733 A137889
Adjacent sequences: A052556 A052557 A052558 * A052560 A052561 A052562
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KEYWORD
| easy,nonn
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AUTHOR
| encyclopedia(AT)pommard.inria.fr, Jan 25 2000
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