A052631 a(n) = n!*Pell(n) (or n!*A000129(n)).

0, 1, 4, 30, 288, 3480, 50400, 851760, 16450560, 357436800, 8629286400, 229162348800, 6638962176000, 208362342988800, 7042436719718400, 255029193619200000, 9851119008546816000, 404305986955014144000, 17569457946995834880000, 805912049524456562688000

Offset

0,3

Links

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

INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 577

Formula

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

Recurrence: {a(1)=1, a(0)=0, (-2-n^2-3*n)*a(n)+(-4-2*n)*a(n+1)+a(n+2)}.

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

Maple

spec := [S, {S=Prod(Z, Sequence(Union(Z, Z, Prod(Z, Z))))}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
with(combstruct):ZL:=[T, {T=Union(Z, Prod(Epsilon, Z, T), Prod(T, Z, Epsilon), Prod(T, Z, Z))}, labeled]:seq(count(ZL, size=i), i=0..19); # Zerinvary Lajos, Dec 16 2007

Crossrefs

Sequence in context: A212073 A172392 A127130 * A368893 A301334 A167139

Adjacent sequences: A052628 A052629 A052630 * A052632 A052633 A052634

Keyword

easy,nonn

Author

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

Status

approved