Project Euler Forum

You're right, I was confused. Sorry about the wrong remark.

Shouldn't the note say that 0! is 1 ?

After all it is just an arbitrary choice made by mathematicians (for good reasons), that a product over an empty set of elements is 1.

Please don't start a new topic for a problem if there exists one already.

Personally I think the choice mathematicians made is not arbitrary, on the contrary.