# Stirling’s approximation

Trying to find a way to calculate the factorials of large (very large) numbers, so as to at least work through my example for Uranium 235 that I considered when working out, for my own benefit, how the binomial distribution worked.

Got this via Twitter:

https://twitter.com/#!/Our_Frank/status/141032793961529344

In fact, wikipedia states the approximation in a slightly less approximate way:

$n! \sim \sqrt{2\pi n} (\frac{n}{e})^n$

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