login
The OEIS is supported by the many generous donors to the OEIS Foundation.

 

Logo
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A052731 E.g.f. [1-x -sqrt(1-2x-3x^2)]/(2x) - [1+x-sqrt(1-2x-3x^2)]/2 . 0
0, 0, 0, 6, 48, 600, 8640, 151200, 3064320, 71124480, 1857945600, 54007430400, 1729195776000, 60483053030400, 2294881337548800, 93889711948032000, 4120492394962944000, 193100926276177920000, 9624765220305371136000 (list; graph; refs; listen; history; text; internal format)
OFFSET
0,4
LINKS
FORMULA
D-finite with recurrence: a(1)=0; a(2)=0; a(3)=6; (-15*n+15*n^3+15*n^2+3*n^4-18)*a(n) +(-n^3-7*n^2-16*n-12)*a(n+1) +(-3*n^2-16*n-21)*a(n+2) +(n+4)*a(n+3)=0; a(4)=48; a(5)=600.
Conjecture: a(n) = n!*A002026(n-2). - R. J. Mathar, Oct 16 2013
a(n) ~ sqrt(2) * 3^(n - 1/2) * n^(n-1) / exp(n). - Vaclav Kotesovec, Nov 19 2021
MAPLE
spec := [S, {C=Prod(B, Z), S=Prod(B, C), B=Union(S, Z, C)}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
CROSSREFS
Sequence in context: A223270 A366339 A365330 * A052711 A113388 A113393
KEYWORD
easy,nonn
AUTHOR
encyclopedia(AT)pommard.inria.fr, Jan 25 2000
STATUS
approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified March 29 02:23 EDT 2024. Contains 371264 sequences. (Running on oeis4.)