Pi Notation

How to I write a function that satisfies the attached formula?

Note that k(sub-n) and u(sub-n) are arrays/lists of size n and each item in the arrays has its own cell. Although, I'm more than willing to modify the data structure if need be.

Another note... big K and little k(sub-n) are different.

Attempting to write the formula here (PI = product notation)...
1/K * { PI[1 + K * kn * un] -1 }

I'm trying to stay away from macros, but if I need to, I'll use them.

Thanks,
JC