Probe

Parker Stevenson is an arrogant millionaire mathmatical genius recluse with a penchant for solving mysteries with his secretary, the only one who was able to answer the riddle to enter his world.

I remember, just, this show and I rather liked it. Initially I thought you were refering to the 'Search' (the pilot was named 'Probe' and I always get them mixed up) that starred Hugh O'Brian, Tony Franciosa, Doug McClure, and Burgess Meredith. Neither of these shows went past one season. So many good ones never do.