Calculators

Math

Factors

15 is the product of the first two odd primes (3 × 5) and represents a quarter hour in minutes. It's a triangular number with 4 factors.

All Factors

The factors of 15 are:  1, 3, 5, 15

The prime factorization is: 15 = 3 x 5

Factoring of 15 Using Trial Division

Find the Factors of 15 :

• Calculate the square root of 15 which is 3.873, and round it down to the closest whole number, 3, and use it in the next step.
• Test the integer values 1 through 3 for division into 15 where the remainder equals 0.
• We find 4 factors where the remainder of division is 0 and they are: 1, 3, 5, 15.

Factor Pairs

1 × 15 = 15
3 × 5 = 15

The factor pairs (multiples) that equal 15 when multiplied together are: (1 and 15), (3 and 5), which we found by matching up all factors of 15 which are: 1, 3, 5, 15.

Is 15 Prime or Composite?

15 is a composite number. Since it has more than two factors, we know that 15 is not prime, it is composite. Prime numbers only have two factors. They are evenly divisible by only 1 and itself.