:gamma(x)
:Func
:Local  z, gamma
:If x<1 Then
:1-x->z
:Else
:x-1->z
:EndIf
:ˆ(2* ¼)*(z+5.5)^(z+.5)*e^(
 -z-5.5)*(1+76.18009173/(z
 +1)-86.50532033/(z+2)+24.
 01409822/(z+3)-1.23173951
 6/(z+4)+.00120858003/(z+5
 )-5.36382E-6/(z+6)->gamma
:If x<1 Then
:(1-x)* (pi symbol)->z
:z/gamma/(sin(zr))->gamma
:EndIf
:
:If gamma (not equal symbol) undef and gamma  (not equal symbol) (infinity symbol)
:round(gamma,10)
:EndFunc
=========
zr is z with small r forcing radian mode

gamma(5)   23.999999996

(n-1)!=gamma(n)
gamma(n) = Integral {0,infinity}, e^(-x)*x^(n-1) dx