This is probably from the early 90s. There's this gang of, I think, outlaws. One of them appears to be capable of doing extreme math in his head. Other members would tell him things like "whats 234423 x 17823", and he would answer on the spot. Later, one of the guys would pick a calculator and see the guy just says random numbers. When he try to call him out on this, the leader of the gang says he is aware of this, but pretends otherwise to keep the guy calm.