  We consider an example of vectorial AdS_5/CFT_4 duality when the boundary
theory is described by N free complex or real Maxwell fields. It is dual to a
particular ("type C") higher spin theory in AdS_5 containing fields in special
mixed-symmetry representations. We extend the study of this theory in
arXiv:1410.3273 by deriving the expression for the large N limit of the
corresponding singlet-sector partition function on S^1 x S^3. We find that in
both complex U(N) and real O(N) invariant cases the form of the one-particle
partition function is as required by the AdS/CFT duality. We also demonstrate
the matching of the Casimir energy on S^3 by assuming an integer shift in the
bulk theory coupling.
