How many paraphyletic groups can be formed from a phylogeny?
If we define a paraphyletic group as any group on a phylogeny that is not monophyletic, I count there to be 2^n - 2*n paraphyletic groups for a fully ladderized tree with n tips.

There are 2^n possible groups of n species. Of these groups, 2*n of them are monophyletic: n groups containing a single species, and n groups containing multiple species.