Is 15 a prime number?

No 15 is not a prime number and on the prime factorization of 15, we get 1, 3, 5, 15 as the factor of 15. The number contains more than two factors, which is 1,3,5 and 10. Hence, it is a composite number. 

If a number to be prime, it has to meet following criteria. The number must hold only 2 divisors when divided. The factors should be number 1 and itself only.

Listed below are some methods to find out whether a particular number is prime or composite?
 

In the counting divisors method, list the divisors of the given number and check if the number, to be considered prime, satisfies the two criteria.

The counting divisors method for 15 would simply be

• Divisors of 15=1,3, 5,15.

• Number of divisors=4

The number 15 can be considered composite.
 

In divisibility method, the prime number only has 2 divisors, which are 1 and itself. There is no specific divisibility check for the number 15 other than checking if it is divisible by 1 and 15.
 

List the prime number chart up to 15.

The prime numbers from 1 to 15 are 1, 2, 3, 5, 7, 11, 13. By keeping a note of the chart like above, we can easily determine if a number is prime or not.
 

Prime factorization is only applicable to non-prime number/composite numbers, Since 15 has more than two factors 1, 3, 5, 15 it can be factored into smaller prime numbers.
 

• Prime Number: A number that can be divided by itself  or 1 is called a prime number.

• Composite Number: A number that can be prime factorized further. It has factors more than itself and 1.

• Prime Factorization: Breaking down a number into its smaller factors is said to be a prime factorization.