How can I calculate a factorial in C# using a library call?

Question

I need to calculate the factorial of numbers up to around 100! in order to determine if a series of coin flip-style data is random, as per this Wikipedia entry on Bayesian p

Answer 1

There has been a previous question on a similar topic. Someone there linked the Fast Factorial Functions web site, which includes some explanations of efficient algorithms and even C# source code.