9 is not a prime number. It can be divided by 3 as well as 1 and 9. The prime numbers below 20 are: 2, 3, 5, 7, 11, 13, 17, 19. Don't forget: the number 1 is not thought of as a prime number.

(The prime number 13, for instance ... A seminal result Green had proved 20 years earlier was “one of the things that brought me into the subject,” Sawhney said. “I was like, ‘Oh man ...

One of my favorite anecdotes about prime numbers concerns Alexander Grothendieck, who was among the most brilliant mathematicians of the 20th century. According to one account, he was once asked ...

How much do you remember about prime numbers from math class? That they’re only divisible by one and themselves? Every other number can be broken down into them? They follow a pattern that ...