• Strange test result

Question related to mission Numbers Factory

Hi folks,

It's my first post. I tried to resolve this task(number-factory), and I got unexpected test result:

SyntaxError: invalid syntax (, line 30), ?, ?_
Fail: checkio(undefined)_

but in description I see: Input: A number N, an integer.

What is undefined value? How I could manage it?

Thank you in advance