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A052635
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E.g.f. (1-3x)/(1-3x-x^2).
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0
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1, 0, 2, 18, 240, 3960, 78480, 1814400, 47940480, 1425029760, 47065536000, 1709915961600, 67769625369600, 2909762279424000, 134544087553075200, 6665534018567424000, 352236213903974400000, 19777072162153033728000
(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 581
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FORMULA
| E.g.f.: (-1+3*x)/(-1+3*x+x^2)
Recurrence: {a(1)=0, a(0)=1, (-2-n^2-3*n)*a(n)+(-6-3*n)*a(n+1)+a(n+2)=0}
Sum(1/13*(-3+11*_alpha)*_alpha^(-1-n), _alpha=RootOf(-1+3*_Z+_Z^2))*n!
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MAPLE
| spec := [S, {S=Sequence(Prod(Z, Z, Sequence(Union(Z, Z, Z))))}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
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CROSSREFS
| Sequence in context: A052726 A155666 A024486 * A168562 A117514 A138437
Adjacent sequences: A052632 A052633 A052634 * A052636 A052637 A052638
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KEYWORD
| easy,nonn
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AUTHOR
| encyclopedia(AT)pommard.inria.fr, Jan 25 2000
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