http://en.wikipedia.org/wiki/P_versus_NP_problem#Problems_in_NP_not_known_to_be_in_P_or_NP-complete We all know it is an usolved problem in computational science But what category does the problem ITSELF belong to?
While it involves Mathematics, it's related to Programming/Communications (Computer Science). If you wanted to categorise it, then you'd likely term it a "Logic problem". I'd suggest "Intelligence and Machines" for that reason if you want the best subforum for it's discussion.
