How to run an expression in CAS mode in program

[webmasterpdx]

Some great suggestions here. BTW, FYI on how g^aMODp is normally calculated (is used a lot in key exchange in encryption algorithms like Diffie Hellman). The algorithm implementation uses the property that
axbMODc = (aMODc x bMODc)MOD c
and
g^2MODp = (gMODp)^2 MOD p
This way, the g^a term never has to fit in a number greater than p. Is a clever trick used in such implementations.
Thanks for all the help.
-Donald