• $0$ (zero) is not a prime a number.
• $1$ is also not a prime number. Although the definition of a prime number seems to apply to 1, you have to count 1 twice -- sorry no 'double dipping' for prime numbers. 1 is not prime.
• $2$ . The number two, $2$, is the only even number that is prime, because all of the other even prime numbers are multiples of 2 and therefore violate the definition of a prime number (only divisible by 1 and itself).
• Read more about how to determine if a number is prime.

• 2 is prime because its only factors are 1 and 2 (2 is the only even prime number).
• 5 is prime because its only factors are 1 and 5.
• 7 is prime because its only factors are 1 and 7.

• 6 is not prime because its factors are factors are 1 ,2, 3, 6.
• 51 is not prime because its factors are factors are 1 , 3 , 17, 51.

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