OFFSET
3,1
COMMENTS
A wheel graph is a graph with n+1 vertices (n>=3) formed by connecting a single vertex to all vertices of an n-cycle. a(n) is the number of labeled wheel graphs. - Geoffrey Critzer, Feb 02 2014
FORMULA
a(n) = Sum_{j=0..n} (-1)^(n-j)*binomial(n,j)*(j+1)^(n+1)/(n+1). - Vladimir Kruchinin, Jun 01 2013
D-finite with recurrence -n*a(n) +(n-1)*(n+1)*a(n-1) = 0. - R. J. Mathar, Feb 01 2022
EXAMPLE
For n >= 1, the sequence is 1, 3/2, 4, 15, 72, 420, 2880, 22680, 201600, 1995840, ...
MATHEMATICA
Table[((n+1)*(n-1)!)/2, {n, 3, 30}] (* Vladimir Joseph Stephan Orlovsky, Apr 03 2011 *)
nn=20; Drop[Range[0, nn]!CoefficientList[Series[x (Log[1/(1-x)]/2+x^2/4+x/2), {x, 0, nn}], x], 4] (* Geoffrey Critzer, Feb 02 2014 *)
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
N. J. A. Sloane, Sep 02 2010
STATUS
approved