Stirling's Approximation

Stirling's Approximation

 

Stirling's approximation gives an approximate value for the factorial function  or the gamma function  for . The approximation can most simply be derived for  an integer by approximating the sum over the terms of the factorial with anintegral, so that

			(1)
			(2)
			(3)
			(4)
			(5)

source :http://mathworld.wolfram.com/StirlingsApproximation.html