Re: factorial of negative numbers

On Tue, Jun 16, 2020 at 08:31:21AM +0100, Dean Rasheed wrote:
>
> Most common implementations do regard factorial as undefined for
> anything other than positive integers, as well as following the
> convention that factorial(0) = 1. Some implementations extend the
> factorial to non-integer inputs, negative inputs, or even complex
> inputs by defining it in terms of the gamma function. However, even
> then, it is undefined for negative integer inputs.

Wow, they define it for negative inputs, but not negative integer
inputs?  I am curious what the logic is behind that.