Why do we talk about “proper factors” but not “proper multiples”?
I had never thought about this before. A colleague and I are thinking about this. My colleague’s guess is that in number theory (the mathematical field that deals with this stuff), there are some things that are true of proper factors that are not true of the number itself, and that this is not a problem with multiples.
But I don’t really know for sure. I’ll find out.