If we take parameters with v values each, and form t-way combinations, each combination can have vt possible settings. The number of these combinations taken from n parameters is C(n, t) = n!/t!(n-t)!, commonly called "n choose t". So the total number of possible t-way combinations of n parameters with v values each is vt * C(n,t).
Consider a small example, with five parameters - a, b, c, d, e - of two values each: 0 or 1. If we take any two, such as (b,e), the possible value settings are 00, 01, 10, 11. We can systematically list the 2-way combinations: (a,b), (a,c), (a,d), (a,e), (b,c), (b,d), (b,e), (c,d), (c,e), (d,e). The number of 2-way combinations is thus 22 * C(5,2) = 40.