Factors of 391

How to find the factors of 391

Test every whole number from 1 up to the square root of 391 (√391 ≈ 19.774). Each number that divides evenly gives you two factors at once: the divisor and the quotient.

• 391 ÷ 1 = 391 — so 1 and 391 are factors
• 391 ÷ 2 = 195.5 — not a whole number
• 391 ÷ 3 = 130.333 — not a whole number
• 391 ÷ 4 = 97.75 — not a whole number
• 391 ÷ 5 = 78.2 — not a whole number
• 391 ÷ 6 = 65.167 — not a whole number
• 391 ÷ 7 = 55.857 — not a whole number
• 391 ÷ 8 = 48.875 — not a whole number
• 391 ÷ 9 = 43.444 — not a whole number
• 391 ÷ 10 = 39.1 — not a whole number
• 391 ÷ 11 = 35.545 — not a whole number
• 391 ÷ 12 = 32.583 — not a whole number
• 391 ÷ 13 = 30.077 — not a whole number
• 391 ÷ 14 = 27.929 — not a whole number
• 391 ÷ 15 = 26.067 — not a whole number
• 391 ÷ 16 = 24.438 — not a whole number
• 391 ÷ 17 = 23 — so 17 and 23 are factors
• 391 ÷ 18 = 21.722 — not a whole number
• 391 ÷ 19 = 20.579 — not a whole number

Collecting both numbers from every successful division gives the complete list: 1, 17, 23 and 391.

Prime factorization of 391

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

The primes you divided by give 391 = 17 × 23. From the exponents you can also count the factors without listing them: (1 + 1) × (1 + 1) = 4.

Properties of 391

• 391 is a composite number.
• The sum of all its factors is 432; the sum of its proper factors (excluding 391) is 41, which makes it a deficient number (its proper factors add up to less than itself).
• 391 is not a perfect square, so its factors pair up evenly.
• Multiples of 391 include 782, 1,173, 1,564, 1,955 and so on.

Factors vs. multiples

Factors of 391 are the numbers that divide into it; multiples of 391 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.