My stepfather (a retired professor) is endlessly fascinated by these kinds of questions. If you ever ask him at dinner "so what are you working on?" the result

My stepfather (a retired professor) is endlessly fascinated by these kinds of questions. If you ever ask him at dinner "so what are you working on?" the result is often a half-hour-long explanation of how many polygons could conceivably fit into some other polygon, if it's not about how many numbers could be derived from some other set of numbers. I've never been able to understand any of it, but it makes him happy.