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A052681
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E.g.f. (1-x)/(1-x-x^2-2x^3+2x^4).
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0
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1, 0, 2, 18, 48, 840, 9360, 90720, 1653120, 25764480, 442713600, 9540115200, 201659673600, 4744989849600, 123531638630400, 3325415917824000, 97123590660096000, 3021564701675520000, 98526128957448192000
(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 629
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FORMULA
| E.g.f.: -(-1+x)/(1-x-2*x^3+2*x^4-x^2)
Recurrence: {a(1)=0, a(0)=1, a(2)=2, (2*n^4+70*n^2+100*n+48+20*n^3)*a(n)+(-18*n^2-52*n-48-2*n^3)*a(n+1)+(-n^2-7*n-12)*a(n+2)+(-n-4)*a(n+3)+a(n+4)=0, a(3)=18}
Sum(-1/353*(-18-106*_alpha+33*_alpha^2+28*_alpha^3)*_alpha^(-1-n), _alpha=RootOf(1-_Z-2*_Z^3+2*_Z^4-_Z^2))*n!
a(n) = n!*A052546(n). - R. J. Mathar, Nov 27 2011
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MAPLE
| spec := [S, {S=Sequence(Prod(Z, Z, Union(Z, Z, Sequence(Z))))}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
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CROSSREFS
| Sequence in context: A009820 A126909 A139268 * A048910 A077591 A050808
Adjacent sequences: A052678 A052679 A052680 * A052682 A052683 A052684
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KEYWORD
| easy,nonn
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AUTHOR
| encyclopedia(AT)pommard.inria.fr, Jan 25 2000
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