Inverse of a Factorial
Factorial: x!=y , 3!=3*2*1=6
Inverse Factorial: x=inv!(y) , inv!(6)=3
Gamma function:gm(x)=(x-1)!
Equation:gm(x)=(x-1)! solving you obtain inv!(gm(x))+1=x
Example:x=5 , inv!(gm(5))+1=x <> inv!(24)+1=5 <> y+1=5 <> y=4
4!=4*3*2*1=24
Based on this , the inverse formula of gamma function is invgm(x)=inv!(x)+1
