Superconformal index of N=3 orientifold theories

We analyze the superconformal index of the N=3 supersymmetric Z_k generalized orientifold theories recently proposed. In the large N limit we derive the index from the Kaluza-Klein modes in AdS_5 x S^5/Z_k, which are obtained from ones in AdS_5 x S^5 by a simple projection. For the ordinary Z_2 orientifold case the agreement with the gauge theory calculation is explicitly confirmed, and for Z_k with k > 2 we perform a few consistency checks with known results for N=3 theories. We also study finite N corrections by analyzing wrapped D3-branes and discrete torsions in the dual geometry.