Byers-Yang theorem

The Byers-Yang Theorem is something math people use to check if a number is a prime number. A prime number is a number that can only be divided by itself and 1. For example, 7 is a prime number because you can't divide it by any number other than itself and 1. The Byers-Yang Theorem is like a checklist to see if a number is a prime number. First you add together all the prime numbers that are less than the number you are checking - this will give you a certain number. If the number you are checking is the same as the number you got from adding all the prime numbers less than it - then that number is a prime number!