My understanding of mathematics is poor, although I'm trying to improve it, so I hope you will forgive me for asking a rather basic question.
I've written a computer code that prints the prime factors of a natural number. It works well. For instance, for the input $72$ it prints $2 \times 2 \times 2 \times 3 \times 3$. On youtube I saw somebody calculate the input $-72$ to $-1 \times 2 \times 2 \times 2 \times 3 \times 3$, so I adjusted my code to accept all whole numbers. But now I'm wondering what to do if the input is $0$.
Should I simply return $0$ (or $1$)? Should I refuse the input?
I tried some online prime factor calculators to see what would happen, but they either ignored/refused input of non-natural numbers, or, in one case, crashed my browser :-)