Why isn't there and math function in VB for finding the factorial of a number ??????

Actually i need to find the following value:

mCn , i.e, m choose n, and the formula for that is

VB Code:
  1. mCn = m! / (m-n)! n!

m factorial / (m-n) factorial * n factorial

n and m always >=1 , How can this be done ???????

Any ideas/codes/comments highly appreciated....,

ashky.