Correct answer for 1<= N <= 9 is N itself. But how is it possible to calculate product of digits for only ONE digit?

c'mon don't be boring, why can't you think that you multiply the digit by nothing?:)) i don't think it's any problem to understand, is it?

But the statement is really incorrect ;)

As we know from set theory, product is defined even for empty set (it equals to 1). The product of one-element set is equal to this element.
The problem statement is correct.

well, never heard about it :) Maybe you're right. But this problem is kinda tricky, considering this thing and that '10' answer for n=0. (I know, it's 100% correct, but... it annoys)