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A052647
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E.g.f. (2-2x-x^2)/((1-2x)(1-x^2)).
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0
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2, 2, 10, 48, 408, 3840, 46800, 645120, 10362240, 185794560, 3719520000, 81749606400, 1962469555200, 51011754393600, 1428416301312000, 42849873690624000, 1371216880889856000, 46620662575398912000
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,1
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LINKS
| INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 593
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FORMULA
| E.g.f.: -(-2+x^2+2*x)/(-1+2*x)/(-1+x^2)
Recurrence: {a(1)=2, a(2)=10, a(0)=2, (12+2*n^3+12*n^2+22*n)*a(n)+(-n^2-5*n-6)*a(n+1)+(-2*n-6)*a(n+2)+a(n+3)=0}
(2^n+Sum(1/2*_alpha^(-n), _alpha=RootOf(-1+_Z^2)))*n!
n!*[2^n+(n mod 2)].
a(n) = n!*A052531(n). - R. J. Mathar, Nov 27 2011
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MAPLE
| spec := [S, {S=Union(Sequence(Prod(Z, Z)), Sequence(Union(Z, Z)))}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
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CROSSREFS
| Sequence in context: A001885 A078433 A059494 * A181334 A032034 A002250
Adjacent sequences: A052644 A052645 A052646 * A052648 A052649 A052650
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KEYWORD
| easy,nonn
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AUTHOR
| encyclopedia(AT)pommard.inria.fr, Jan 25 2000
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