0.577215664901 var gamma
-0.65587807152056 var coeff
-0.042002635033944 var quad
0.16653861138228 var qui
-0.042197734555571 var theSet

def recigamma var z /# n -- n #/
    z 6 power theSet *
    z 5 power qui *
    z 4 power quad *
    z 3 power coeff *
    z 2 power gamma *
    z + + + + +
enddef

/# without var
def recigamma
    dup 6 power theSet * swap
    dup 5 power qui * swap
    dup 4 power quad * swap
    dup 3 power coeff * swap
    dup 2 power gamma * swap
    + + + + +
enddef
#/

def gammafunc   /# n -- n #/
    dup 1 == if
    else
        dup abs 0.5 <= if
            recigamma 1 swap /
        else
            dup 1 - gammafunc swap 1 - *
        endif
    endif
enddef

0.1 2.1 .1 3 tolist
for
    dup print " = " print gammafunc print nl
endfor