This is a fun list of unsolved mathematical problems, described by professional mathematicians who are working on them, ranging from the easily understood (are there any odd perfect numbers?) to some arcane questions in number theory and topology.

[One peculiar typo, at least at the time I’m posting this: y^2 = x^5 – x + 1 is obviously *not* solved by x=0, y=0. I guess they meant x=0, ±1, y=±1.]

https://www.scientificamerican.com/article/9-unsolved-mysteries-in-mathematics/