Of course, this only works for n mod 5 = 0, which leaves out a heck of a lot of possibilities.

Teproc: the exclamation points in the formula represent the factorial function. That's the product of all whole numbers from the number down; so, for 5, it's 5 × 4 × 3 × 2 × 1 = 120. Because the way the OP has this set up results in huge factorials (15! has 13 digits), it helps to break it down and cancel things out a bit. For theory's question, t = 2, n = 15, we have:

n/5 = 3

5^{t} = 25

The first factorial on top is 3!, and the first on the bottom is 1!. Divide those and you get 3 × 2 = 6

The second factorial on top is 13!, and the second on the bottom, n!, is 15!. Divide them, and you get 15 × 14 = 210 (on the bottom).

Simplified, then, the fraction is (6 × 25)/(210) = 0.714

Therefore, p (the chance of getting 2 Maps this cycle) is 0.286, or about 29%.