I'm trying to calculate $\displaystyle \zeta$(4,$\displaystyle \frac{1}{2}$)

I used $\displaystyle \zeta $(s,a) = $\displaystyle \Gamma $(1-s) I(s,a)

Am I right by saying $\displaystyle \Gamma $(1-s) is undefined for s=4 and

I(4, 1/2) = 0 as s is a positive whole number

So $\displaystyle \zeta $ (4, 1/2) =0

Am I doing this right or am I just making a mess of this

Thanks in advance