%N Number of (unlabeled) loopless multigraphs with no isolated vertices such that the sum of the numbers of vertices and edges is n.
%C Also the number of skeletal 2-cliquish graphs with n vertices and no isolated vertices. See Einstein et al. link below.
%H Andrew Howroyd, <a href="/A265580/b265580.txt">Table of n, a(n) for n = 0..100</a>
%H D. Einstein, M. Farber, E. Gunawan, M. Joseph, M. Macauley, J. Propp and S. Rubinstein-Salzedo, <a href="https://arxiv.org/abs/1510.06362">Noncrossing partitions, toggles, and homomesies</a>, arXiv:1510.06362 [math.CO], 2015.
%F a(n) = A265581(n) - A265581(n-1), n>=1.
%e 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.
%Y Cf. A265581.
%A _Michael Joseph_, Dec 10 2015
%E Terms a(19) and beyond from _Andrew Howroyd_, Feb 01 2020