www.reference.com/article/number-1-prime-fcb2c1bd64c065d1

The number one is neither prime nor composite. Prime numbers are those defined as natural numbers greater than one not divisible by any other numbers but one and itself. Composite numbers have at least one additional positive divisor and include all whole numbers greate...

www.reference.com/article/number-2-prime-589a9996b96a8b2f

The number 2 is a prime number. It is the smallest prime number and the only even number that is prime. Its only two factors are 1 and 2.

www.reference.com/article/two-prime-number-e424a94a55b2cf3a

Two is a prime number. Two is the smallest prime number and the only even prime number, since all other even numbers divide by two.

www.reference.com/article/15-prime-number-9c4b015fd8478e0f

Fifteen is not a prime number. A prime number is a positive number that has only two possible divisors, 1 and itself. Fifteen can be divided by 3 and 5 as well as 1 and itself.

www.reference.com/article/prime-factorization-54-d0af8c4d31cef5d5

The prime factorization of 54 is 2 x 3 x 3 x 3, which can also be written as 2 x 33. Prime factors are the prime numbers that are multiplied to get another number. A prime number is any number that can only be divided by itself and 1, such as 3, 5 and 17; numbers that c...

www.reference.com/article/21-prime-number-12e5677deb89b62

The number 21 is not a prime number. Prime numbers are numbers greater than one that are evenly divisible by only 1 and themselves. As the number 21 has multiple factors, including 1, 21, 3 and 7, it does not meet the definition of a prime number.

www.reference.com/article/one-prime-number-4c916ba7da91e2fa

One is not a prime number because the definition of a prime number is any number that is greater than one that is only divisible by one and itself. Since one is of course not greater than one, it does not fit the definition of a prime number.