GAMMA(x) returns the Gamma function of x.
When the argument n is an integer, the gamma function is similar to the factorial function, offset by one. Gamma(n) is defined as:
When x is a real number Gamma(x) is defined by the integral:
The argument n must be higher than 0.
If n is larger than 171.62, the function overflows and returns an error. For large arguments the GammaLn function can be used.