|
Search: id:A052685
|
|
|
| A052685 |
|
A simple regular expression in a labeled universe. |
|
+0
1
|
|
| 1, 1, 4, 24, 168, 1680, 18720, 252000, 3830400, 65681280, 1251936000, 26225337600, 599710003200, 14851444608000, 396138155212800, 11320537003776000, 345079573622784000, 11176410365632512000
(list; graph; listen)
|
|
|
OFFSET
|
0,3
|
|
|
LINKS
|
INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 633
|
|
FORMULA
|
E.g.f.: -(-1+x^2)/(1-2*x^2+x^4-x)
Recurrence: {a(1)=1, a(0)=1, a(2)=4, a(3)=24, (n^4+35*n^2+50*n+24+10*n^3)*a(n)+(-2*n^2-14*n-24)*a(n+2)+(-n-4)*a(n+3)+a(n+4)}
Sum(-1/283*(-112*_alpha+48*_alpha^3-9*_alpha^2-27)*_alpha^(-1-n), _alpha=RootOf(1-2*_Z^2+_Z^4-_Z))*n!
|
|
MAPLE
|
spec := [S, {S=Sequence(Prod(Z, Union(Z, Sequence(Prod(Z, Z)))))}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
|
|
CROSSREFS
|
Sequence in context: A059304 A069722 A027079 this_sequence A032349 A103334 A156017
Adjacent sequences: A052682 A052683 A052684 this_sequence A052686 A052687 A052688
|
|
KEYWORD
|
easy,nonn
|
|
AUTHOR
|
encyclopedia(AT)pommard.inria.fr, Jan 25 2000
|
|
|
Search completed in 0.002 seconds
|
