I am trying to find an ordinary generating function using Flajolet's symbolic method to count unlabelled connected graphs with $n$ nodes (OEIS A001349).
I can't see which constructions can correspond ($\text{Seq}(\mathcal{Z}), \text{Set}(\mathcal{Z}),$etc) or some functional equation.
I have not been able to find help in any bibliography, I understand that the generating function must be seen in the form $1+x+x^2+2x^3+6x^4+...$
I am interested in finding a general formula for the ordinary generating function to obtain these coefficients. Does anyone have a bibliography of which constructions of the symbolic method can help me? or in this case the symbolic method does not apply?
