1. The problem statement, all variables and given/known data Can someone explain the notation of the integer ring(Z)? My friend's in Math 100 and has questions on Z. I have never heard of ring's before and I'm at a loss to help him. From what I've gathered Z is a set of all integers. They ask for the invertible elements in different Zn like Z1 Zi Z101 if someone could explain how to identify invertible elements in the different Zn would be great. They also ask him to "Factor 5 + i over Z." 3. The attempt at a solution I've tried to look up rings, but I don't understand how you would factor a number over a set especially when it has an imaginary in there, haven't really worked with them that much. No text for the class and no explanation from the instructor.