Jerry Seinfeld, he was doing Letterman show all the time, so he kind of had an excuse, that people know the jokes already. He didn't have time to do stand-up. A guy like me, I have no excuses.
Mathematics is much more than computation with pencil and a paper and getting answers to routine exercises. In fact, it can easily be argued that computation, such as doing long division, is not mathematics at all. Calculators can do the same thing and calculators can only calculate they cannot do mathematics.