The number 57 is not a prime number because it can be divided evenly by numbers other than 1 and itself. Specifically, 57 can be divided by 3 and 19, as 3 × 19 = 57. Therefore, it has factors of 1, 3, 19, and 57. In contrast, a prime number is defined as a natural number greater than 1 that has no positive divisors other than 1 and itself. Examples of prime numbers include 2, 3, 5, and 7. These numbers are fundamental in number theory and have unique properties that make them important in various mathematical applications.