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A052850
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A simple grammar.
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1
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0, 2, 5, 20, 114, 864, 8280, 96480, 1325520, 20966400, 374855040, 7468070400, 163938297600, 3929729126400, 102104460057600, 2857878742118400, 85719362496768000, 2742726680838144000, 93247371837075456000, 3356802948155424768000, 127556444063199191040000
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,2
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LINKS
| INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 818
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FORMULA
| E.g.f.: (-x-ln((-1+x)/(-1+2*x))+ln((-1+x)/(-1+2*x))*x)/(-1+x).
Recurrence: {a(1)=2, a(2)=5, a(3)=20, a(4)=114, (2*n^3-2*n)*a(n)+(-3*n^2+2*n+5)*a(n+1)+(-2+n)*a(n+2)}.
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MAPLE
| spec := [S, {B=Sequence(Z, 1 <= card), C=Cycle(B), S=Union(B, C)}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
a:= n-> `if`(n=0, 0, (2^n+n-1)*(n-1)!): seq (a(n), n=0..25); # Alois P. Heinz, Nov 09 2011
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CROSSREFS
| Bisection of A199660. - Alois P. Heinz, Nov 09 2011
Sequence in context: A129949 A127065 A168357 * A000130 A009599 A112833
Adjacent sequences: A052847 A052848 A052849 * A052851 A052852 A052853
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KEYWORD
| easy,nonn
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AUTHOR
| encyclopedia(AT)pommard.inria.fr, Jan 25 2000
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