475796domain: NAppears in sequencesa(n) = 2/n^2*( sum_{k=0..n-1} (2*k+1)*C(n-1,k)^2*C(n+k,k) ), where C(m,k) denotes the binomial coefficient m!/(k!*(m-k)!).at n=7A246542Number of directed multigraphs including self-loops on n vertices and n edges.at n=8A362387