Introduction to number theory lecture 11. Euler's theorem

This lecture is part of my Berkeley math 115 course "Introduction to number theory" For the other lectures in the course see https://www.youtube.com/playlist?list=PL8yHsr3EFj53L8sMbzIhhXSAOpuZ1Fov8 This lecture covers Euler's generalization of Fermat's theorem. The textbook is "An introduction to the theory of numbers" by Niven, Zuckerman, and Montgomery (5th edition).