A052606 E.g.f. (1-x)^2/(1-4x+x^2).

1, 2, 16, 180, 2688, 50160, 1123200, 29342880, 876072960, 29425939200, 1098191001600, 45083550758400, 2019049224192000, 97957525739673600, 5118154482618777600, 286518188551795200000, 17108806991486386176000

Offset

0,2

Links

Table of n, a(n) for n=0..16.

INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 551

Formula

E.g.f.: (-1+x)^2/(1-4*x+x^2)

Recurrence: {a(0)=1, a(1)=2, (n^2+3*n+2)*a(n)+(-4*n-8)*a(n+1)+a(n+2)=0, a(2)=16}

Sum(-1/3*(-1+2*_alpha)*_alpha^(-1-n), _alpha=RootOf(1-4*_Z+_Z^2))*n!

Maple

spec := [S, {S=Sequence(Prod(Sequence(Z), Sequence(Z), Union(Z, Z)))}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);

Crossrefs

Sequence in context: A217360 A371669 A363311 * A011553 A291816 A123898

Adjacent sequences: A052603 A052604 A052605 * A052607 A052608 A052609

Keyword

easy,nonn

Author

encyclopedia(AT)pommard.inria.fr, Jan 25 2000

Status

approved