On: Defining zero factorial

[rspeer]

It's awesome and weird that there's a consistent and useful function that lets you define an equivalent to (-1/2)! -- and that what you get is the square root of pi.

[SamReidHughes → rspeer]

Of course it has pi in it. Otherwise it'd have to have e in it.

[mturmon → rspeer]

I agree. The Stirling formula is another place where the square root of pi pops out from factorials.