How do you know if a number is a prime number?

When your looking for a prime number, you have to know that the number has to be greater than 1, and only obtains two factors (namely 1 and the number itself). Now to begin learning how to find a prime number. Example: Find out whether 337 is a prime number or not? Step 1: 19 square root (337) Prime numbers less than 19 are 2, 3, 5, 7, 11, 13, 17 Step 2: 337 is not divisible by any of them Therefore 337 is a prime number