Maxima Function
genfact (x, y, z)
Returns the generalized factorial, defined as x (x-z) (x - 2 z) ... (x - (y - 1) z). Thus, for integral x, genfact (x, x, 1) = x! and genfact (x, x/2, 2) = x!!.
x (x-z) (x - 2 z) ... (x - (y - 1) z)
genfact (x, x, 1) = x!
genfact (x, x/2, 2) = x!!