OFFSET
1,2
REFERENCES
F. Harary and E. M. Palmer, Graphical Enumeration, Academic Press, NY, 1973.
LINKS
Max Alekseyev, Table of n, a(n) for n = 1..40
FORMULA
G.f.: f(x)*x/(1 + x) where f(x) is the g.f. of A339064. - Andrew Howroyd, Nov 22 2020
EXAMPLE
a(3)=7: the triangular graph with one edge rooted. The disconnected graph of the connected linear graph with 3 nodes aside the connected graph with 2 nodes, 2 choices for the root. The three disconnected graphs with 3 graphs on 2 nodes, one of the three with the root. The connected star graph with one edge rooted. The connected linear graph with four nodes, 2 choices for the root. - R. J. Mathar, May 03 2018
PROG
(PARI) \\ See A339063 for G.
seq(n)={my(A=O(x*x^n)); Vec((G(2*n, x+A, [1, 1]) + G(2*n, x+A, [2]))/(2*(1+x)))} \\ Andrew Howroyd, Nov 21 2020
CROSSREFS
KEYWORD
nonn
AUTHOR
Vladeta Jovovic, Mar 07 2007
EXTENSIONS
Terms a(10) onward from Max Alekseyev, May 03 2018
STATUS
approved