I don't know how to type subscripts here, so K(m,n)Let $K(m,n)$ denotes the complete bipartite graph on parts of cardinality m$m$ and n$n$.
My question is; How many nonisomorphic spanning subgraphs are there of of K(m,n)$K(m,n)$? This is such an obvious question, it has probably been answered. I just don't know wheretowhere to look. There is an obvious, but complex to use, recursion for the constructions. Given the set of nonisomorphic subgraphs of K(m-1,n)$K(m-1,n)$ -- or of Km,n-1)$K(m,n-1)$ -- appending the n-1$n-1$ edges from the missing vertex in the first case or m-1$m-1$ in the second edges in all inequivalent ways will generate the set for K(m,n)$K(m,n)$. But this is not a numerical problem so no simple recursion seems possible -- yet it may have well been solved using Polya's counting theorem. Do any of you know the answer, or where it can be found?