I saw this approximation in some notes:
$n! \approx e^{-n}*n^n*\sqrt{2\pi n}$
What is this approximation? How is it derived? Is it a known formula?
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2See Stirling's formula. – Michael Burr Jul 22 '17 at 17:47
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3See Stirling's approximation – MAN-MADE Jul 22 '17 at 17:48
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2Note that:$$\ln(n!)=\sum_{k=2}^n\ln(k)$$and then apply the Euler-Maclaurin formula – Simply Beautiful Art Jul 22 '17 at 17:49