Factorial x ( x! )
By Recursion Formula (Recursion)
By Stirling's Theorem
( x! = (x / e) x*(2PI.x)1/2 ( 1 + 1/12x + 1/228x² - 139 / 51840x3 + ......... )
  Enter the x value
  Find x! (Stirling Approximation)
  Find discount ( 1 + 1/12x + 1/228x² - 139 / 51840x3 + ..)
  Find x! (Stirling Formula)
  Find x !(recursion)
Find Error % in Stirling Formula
Find Error % in Stirling Approximation