@bielle It's useful if you're using it inline. It's not meant to return the prime number.
@ssimar If you're going to reply with a blatant, and disrespectful comment, don't bother leaving one.

A very useful resource in finding prime numbers is stronger encryption. As there are only so many factors when multiiplying them. When multiplying two prime numbers together instead of any two ordinary numbers, there are only four factors, making the encryption key stronger, which makes it harder to crack.