A052595 E.g.f. 1/(1-3x-x^2).

1, 3, 20, 198, 2616, 43200, 856080, 19792080, 522950400, 15544690560, 513406252800, 18652322304000, 739253228313600, 31740638183654400, 1467650891266560000, 72709824125562624000, 3842307771930980352000

Offset

0,2

Links

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

INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 540

Formula

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

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

Sum(1/13*(2*_alpha+3)*_alpha^(-1-n), _alpha=RootOf(-1+3*_Z+_Z^2))*n!

a(n)= n!*A006190(n+1). - R. J. Mathar, Nov 27 2011

Maple

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

Crossrefs

Sequence in context: A158833 A296715 A054361 * A367924 A363136 A244491

Adjacent sequences: A052592 A052593 A052594 * A052596 A052597 A052598

Keyword

easy,nonn

Author

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

Status

approved