Introduction to number theory lecture 6. Multiplicative functions.

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 We give some examples of multiplicative functions and show how to calculate them. As an application we discuss even perfect numbers. The textbook is "An introduction to the theory of numbers" by Niven, Zuckerman, and Montgomery (5th edition).