Having trouble with symprod

Hi

I would like to run the following:

K=3;
Ck_vec=[2 3 3];
Ck_vec=int64(Ck_vec)
mk_vec=[4 4 4];
mk_vec=int64(mk_vec)
syms k;
symprod(nchoosek((Ck_vec(k)-1+mk_vec(k)),(Ck_vec(k)-1)),k,1,K)

But it keeps returning an error and I am not sure what to do to fix it.

Any help appreciated.

Thanks,

Erin