What is the impossible equation that Jean Luc Picard tells Riker in Star Trek TNG?

I remember it being in an early episode where Riker didn't have a beard, but I don't remember what episode it was and what the equation was, only that at some point Picard said 'factor of three'. Anyone know the equation or the episode or (preferably) both? I think it had something to do with a french mathematician, but I might be wrong.