A052637 E.g.f. 3x(1+x-x^2)/(1-x).

0, 3, 12, 18, 72, 360, 2160, 15120, 120960, 1088640, 10886400, 119750400, 1437004800, 18681062400, 261534873600, 3923023104000, 62768369664000, 1067062284288000, 19207121117184000, 364935301226496000

Offset

0,2

Links

Table of n, a(n) for n=0..19.

INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 583

Formula

E.g.f.: 3*(-x+x^2-1)*x/(-1+x)

Recurrence: {a(0)=0, (-1-n)*a(n)+a(n+1)=0, a(1)=3, a(3)=18, a(2)=12}

3*n!, n>2.

Maple

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

Crossrefs

Sequence in context: A348169 A342785 A166038 * A120623 A158517 A043877

Adjacent sequences: A052634 A052635 A052636 * A052638 A052639 A052640

Keyword

easy,nonn

Author

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

Status

approved