A052594 E.g.f. x(1+x-2x^2)/(1-2x).

0, 1, 6, 24, 192, 1920, 23040, 322560, 5160960, 92897280, 1857945600, 40874803200, 980995276800, 25505877196800, 714164561510400, 21424936845312000, 685597979049984000, 23310331287699456000

Offset

0,3

Links

Table of n, a(n) for n=0..17.

INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 539

Formula

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

Recurrence: {a(1)=1, a(0)=0, (-2*n-2)*a(n)+a(n+1)=0, a(2)=6, a(3)=24}

2^(n-1)*n!, n>2.

Maple

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

Crossrefs

Sequence in context: A064049 A336267 A018981 * A372136 A320944 A277985

Adjacent sequences: A052591 A052592 A052593 * A052595 A052596 A052597

Keyword

easy,nonn

Author

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

Status

approved