Is it possible to get a perfect square if you multiply three consecutive natural numbers?
Webster was not a mathematician. Mathematically speaking, though there may be some debate over the classification of zero, there has yet been no adopted convention. Consequently, when zero is to be excluded, to avoid confusion, the author may specify, "positive integers" or "nonnegative integers." I do not know what this author's position on 'zero' is. However, since he just requested "natural numbers", I will stand behind my answer.