A useful thing to find would be a CUDA (or, ideally, an OpenCL, which runs on both nVidia and AMD) program that performs fast modular exponentiation of large numbers (i.e. larger than 64 bits; the numbers needed are on the order of 256 bits or larger).  Modular exponentiation is at the heart of both the Fermat Primality Test and the various forms of the Euler Lagrange Lichfitz Test.