OFFSET
0,6
COMMENTS
LINKS
Andrew Howroyd, Table of n, a(n) for n = 0..100
D. Einstein, M. Farber, E. Gunawan, M. Joseph, M. Macauley, J. Propp and S. Rubinstein-Salzedo, Noncrossing partitions, toggles, and homomesies, arXiv:1510.06362 [math.CO], 2015.
FORMULA
From Andrew Howroyd, Feb 01 2020: (Start)
a(n) = Sum_{k=1..ceiling(n/2)} A191646(n-k, k) for n > 0.
Inverse Euler transform of A265581. (End)
EXAMPLE
For n = 5, the a(5) = 2 such multigraphs are the graph with three vertices and edges from one vertex to each of the other two, and the graph with two vertices connected by three edges.
PROG
(PARI) \\ See A191646 for G, InvEulerMT.
seq(n)={my(v=InvEulerMT(vector((n+1)\2, k, 1 + y*Ser(G(k, n-1), y)))); Vec(1 + sum(i=1, #v, v[i]*y^i) + O(y*y^n))} \\ Andrew Howroyd, Feb 01 2020
CROSSREFS
KEYWORD
nonn
AUTHOR
Michael Joseph, Dec 10 2015
EXTENSIONS
Terms a(19) and beyond from Andrew Howroyd, Feb 01 2020
STATUS
approved