Permutations without overflow

The use of the factorial function in computing permutations and combinations has overflow problems that are avoided by these two functions.

The use of the factorial function in computing nPr = n!/(n-r)! or in computing nCr = n!/((n-r)!*r!) has overflow problems when n>170 on a 64-bit machine.
These two functions: Perm(n,r) and Comb(n,r) avoid the overflow problem.
nPr is defined as Perm(n,r) and nCr is defined as Comb(n,r).

Example:
If n=171, factorial(n) = Inf on a 64-bit machine.
Therefore, neither P(171,15) nor C(171,15) can be evaluated directly.
Perm(171,15) = 1.6611e33, and
Comb(171,15) = 1.2703e21.
Likewise,
Perm(1000,49) = 3.0256e+146, and
Comb(171,15) = 4.9740e+83.

These two functions are useful in predicting the outcomes of Bernoulli experiments that utilize the binomial distribution.