|
| |
|
|
A052555
|
|
E.g.f. 1/(1-2x-x^2).
|
|
0
| |
|
|
1, 2, 10, 72, 696, 8400, 121680, 2056320, 39715200, 862928640, 20832940800, 553246848000, 16027872537600, 503031194265600, 17001946241280000, 615694938034176000, 23782705115000832000, 976080997055324160000
(list; graph; refs; listen; history; internal format)
|
|
|
|
OFFSET
| 0,2
|
|
|
LINKS
| INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 496
|
|
|
FORMULA
| E.g.f.: -1/(-1+2*x+x^2)
Recurrence: {a(0)=1, a(1)=2, (-2-n^2-3*n)*a(n)+(-4-2*n)*a(n+1)+a(n+2)=0}
Sum(1/4*(1+_alpha)*_alpha^(-1-n), _alpha=RootOf(-1+2*_Z+_Z^2))*n!
a(n) = n!*A000129(n+1). - R. J. Mathar, Nov 27 2011
|
|
|
MAPLE
| spec := [S, {S=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, i=1..18); - Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), Dec 16 2007
|
|
|
CROSSREFS
| Sequence in context: A060842 A111554 A177384 * A204808 A084844 A144011
Adjacent sequences: A052552 A052553 A052554 * A052556 A052557 A052558
|
|
|
KEYWORD
| easy,nonn
|
|
|
AUTHOR
| encyclopedia(AT)pommard.inria.fr, Jan 25 2000
|
| |
|
|
