Factors of 15

How to find the factors of 15

Test every whole number from 1 up to the square root of 15 (√15 ≈ 3.873). Each number that divides evenly gives you two factors at once: the divisor and the quotient.

• 15 ÷ 1 = 15 — so 1 and 15 are factors
• 15 ÷ 2 = 7.5 — not a whole number
• 15 ÷ 3 = 5 — so 3 and 5 are factors

Collecting both numbers from every successful division gives the complete list: 1, 3, 5 and 15.

Prime factorization of 15

Divide by the smallest prime that fits, and keep going until the quotient is 1:

The primes you divided by give 15 = 3 × 5. From the exponents you can also count the factors without listing them: (1 + 1) × (1 + 1) = 4.

Properties of 15

• 15 is a composite number.
• The sum of all its factors is 24; the sum of its proper factors (excluding 15) is 9, which makes it a deficient number (its proper factors add up to less than itself).
• 15 is not a perfect square, so its factors pair up evenly.
• Multiples of 15 include 30, 45, 60, 75 and so on.

Factors vs. multiples

Factors of 15 are the numbers that divide into it; multiples of 15 are the numbers it divides into. Every number has a limited set of factors but infinitely many multiples. To work with any other number, use the factors calculator, or find shared factors with the GCF calculator.