A052602 E.g.f. x^2*(1-x)/(1-x-x^2).

0, 0, 2, 0, 24, 120, 1440, 15120, 201600, 2903040, 47174400, 838252800, 16286054400, 342486144000, 7758867916800, 188305108992000, 4875010043904000, 134094160392192000, 3905447960494080000

Offset

0,3

Links

Table of n, a(n) for n=0..18.

INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 547

Formula

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

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

Sum(1/5*(-4+7*_alpha)*_alpha^(-1-n), _alpha=RootOf(-1+_Z+_Z^2))*n!

Maple

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

Mathematica

With[{nn=30}, CoefficientList[Series[(x^2*(1-x))/(1-x-x^2), {x, 0, nn}], x] Range[0, nn]!] (* Harvey P. Dale, Dec 21 2011 *)

Crossrefs

Sequence in context: A365980 A052607 A375414 * A012588 A012290 A012591

Adjacent sequences: A052599 A052600 A052601 * A052603 A052604 A052605

Keyword

easy,nonn

Author

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

Status

approved