A052667 E.g.f. 1/(1-2x-x^4).

1, 2, 8, 48, 408, 4320, 54720, 806400, 13587840, 257644800, 5428684800, 125817753600, 3181049625600, 87128475033600, 2570016024576000, 81222270345216000, 2738060898693120000, 98070849049485312000

Offset

0,2

Links

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

INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 615

Formula

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

Recurrence: {a(0)=1, a(1)=2, a(2)=8, a(3)=48, (-n^4-35*n^2-50*n-24-10*n^3)*a(n)+(-2*n-8)*a(n+3)+a(n+4)=0}

Sum(1/86*(27+18*_alpha^3+12*_alpha^2+8*_alpha)*_alpha^(-1-n), _alpha=RootOf(-1+2*_Z+_Z^4))*n!

a(n) = n!*A008999(n). - R. J. Mathar, Nov 27 2011

Maple

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

Crossrefs

Sequence in context: A063075 A177386 A112541 * A327904 A006925 A185135

Adjacent sequences: A052664 A052665 A052666 * A052668 A052669 A052670

Keyword

easy,nonn

Author

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

Status

approved