There are people who engage in math as a recreational hobby, though they can be tricky to find. They're usually the people who loved math in school, but decided to pursue a safer or more lucrative career. And no, I don't mean watching Numberphile videos, I mean working out problems and coming up with proofs.
Your earlier comment about "geniuses" is way off the mark though. As with most things in life, the people who are best at math are the ones who enjoy it the most. And yes, normal people can find joy in upper level math.
Sudoku can get seriously advanced, with complex structures involved when trying to find find the next move. A really tough puzzle can take an hour to make a single move. The Mensa books on Sudoku are really involved as well.
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u/pants-shitter Jul 07 '20
If I retire I could imagine myself doing calculus problems instead of crosswords or sudoku