Welcome! Math phd-student here. Will be following you :)
Note that for every positive number greater than 1, we can find a prime number that divides it is part of the fundamental theorem of arithmetic which also requires a proof. Idea for a second post?
It's part of FToA, without the uniqueness of the factors. This piece is quite hard to write since I kind of had to hand-wave that part here. I did went on without explaining why prime divisors always exist, so maybe, just for completion I'd talk about FToA in my next post. Thanks.