I'm pretty sure that the definition of the factorial operation in mathematics requires an integer. Yet google seems to disagree. I messed up the formatting of a calculation I was using google to compute and it ended up calculating the factorial of an irrational number. I'm just wondering how exactly would one do that?
I'm sure it wouldn't be impossible to find a different formula that would only make sense if 0!=0. Then what? Sure, they wouldn't both be equally useful, but there would be no logical way to choose one definition over the other.