I've been having trouble finding many pure math Ph.D. programs with active research groups in the general field of discrete mathematics (perhaps due to its interdisciplinary nature). I'm only aware of the top schools in this field (e.g. Carnegie Mellon, Georgia Tech, UCSD, Rutgers); can anyone suggest some middle-to-lower ranked schools with a relatively large presence in discrete math? If it helps, I am particularly interested in graph theory, as well as connections between combinatorics/graph theory to number theory and topology. My interests are entirely within the domain of pure math; I do not wish to apply to any applied math or computer science programs. Thank you!