|
| |
|
|
A052503
|
|
Number of permutations sigma without fixed point such that sigma^4=Id.
|
|
0
| |
|
|
1, 1, 9, 105, 2625, 76545, 3440745, 176080905, 12034447425, 922995698625, 87505195602825
(list; graph; refs; listen; history; internal format)
|
|
|
|
OFFSET
| 0,3
|
|
|
LINKS
| INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 28
|
|
|
FORMULA
| E.g.f.: exp(1/2*x^2+1/4*x^4)
Recurrence: {a(1)=0, a(0)=1, a(2)=1, a(3)=0, (-11*n-6-n^3-6*n^2)*a(n)+(-n-3)*a(n+2)+a(n+4)}
a(n) = 2^n*GAMMA(n+1/2)*A047974(n)/Pi^(1/2) - Mark van Hoeij, Oct 30 2011.
|
|
|
MAPLE
| spec := [S, {S=Set(Union(Cycle(Z, card=2), Cycle(Z, card=4)))}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
|
|
|
CROSSREFS
| Sequence in context: A081461 A110698 A012485 * A122569 A039619 A080505
Adjacent sequences: A052500 A052501 A052502 * A052504 A052505 A052506
|
|
|
KEYWORD
| easy,nonn
|
|
|
AUTHOR
| encyclopedia(AT)pommard.inria.fr, Jan 25 2000
|
| |
|
|
