Calculating the Factorials of Large Numbers
Thomas Szirtes · IEEE Transactions on Reliability · 1984
The sharpened Stirling's formula approximates well the factorial of a large number N. The relative error of this approximation decreases with the magnitude of N and is about 10-7for the factorial of 101. The upper limit of the method is about N = 108. The program listing and execution protocol of the routine for a HP41C programmable calculator are presented.