Eli5 why we cant have negative factorials?

Question

I looked it up on google but my extent of math goes to algebra 2, but it immediately went into wacky stuff like “the gamma function”, simply put, what is the gamma function and why is it stopping stuff like -9! From being -362880

In: 2

Answer 1

Factorial involves multiplying an integer by every integer between itself and one

i.e. n * (n-1) * (n-2) * … * 1

So 9! = 9 * 8 * 7 * 6 * 5 * 4 * 3 * 2 * 1

If you start with a negative value of n and keep subtracting 1 then you’ll never get to 1.