OFFSET
0,2
COMMENTS
Since almost all such graphs are connected a(n) is asymptotic to 2*A006125.
LINKS
Alois P. Heinz, Table of n, a(n) for n = 0..81
FORMULA
MAPLE
b:= n-> 2^(n*(n-1)/2):
a:= n-> (t-> add(`if`(j=t, 1, 2)*b(j)*b(n-j)
*binomial(n, j), j=0..t))(n/2):
seq(a(n), n=0..20); # Alois P. Heinz, Aug 01 2016
MATHEMATICA
nn=15; g=Sum[2^Binomial[n, 2] x^n/n!, {n, 0, nn}]; Range[0, nn]! CoefficientList[Series[g^2, {x, 0, nn}], x]
CROSSREFS
KEYWORD
nonn
AUTHOR
Geoffrey Critzer, Jun 17 2013
STATUS
approved