OFFSET
0,2
COMMENTS
a(0) = 1 by convention. Loops add two to the degree of a node.
a(n) is also the number of connected multigraphs on 2*n+1 unlabeled nodes with one vertex of degree 2 and all others of degree 3, loops allowed.
EXAMPLE
The a(1) = 3 multigraphs correspond to either a triple edge rooted on one of the edges or to a single edge with a loop at each end and rooted on either the edge or the loop.
CROSSREFS
KEYWORD
nonn
AUTHOR
Andrew Howroyd, Mar 12 2023
STATUS
approved