What are the factor pairs of 18?

The pairs are (1, 18), (2, 9) and (3, 6). Each pair multiplies to 18.

What is the greatest common factor of 18 and 24?

The GCF of 18 and 24 is 6. The common factors are 1, 2, 3 and 6, and 6 is the largest.

Factors of 18 - Factor Pairs & Prime Factorization

Q: What are the factors of 18?

The factors of 18 are 1, 2, 3, 6, 9 and 18. That is six factors, and each one divides 18 exactly.

Q: What is the prime factorization of 18?

18 = 2 × 3 × 3 = 2 × 3². Its prime factors are 2 and 3.

What Are the Factors of 18?

A golf course has 18 holes, and you can play them as 2 loops of 9 or 3 loops of 6 with none left over. Every one of those tidy splits is a factor: a whole number that divides another number exactly, with no remainder.

The factors of 18 are 1, 2, 3, 6, 9 and 18. That is six factors.

Factor Pairs of 18

Look for pairs that multiply to 18, working from the outside in.

Handwritten notebook page titled Factors of 18 showing 1 × 18, 2 × 9, 3 × 6 all equal to 18, with the six factors 1, 2, 3, 6, 9 and 18 circled in red and the note 6 factors — The 3 pairs of 18, with every factor circled.

Start with 1 × 18.
Try 2. Since 18 ÷ 2 = 9, write 2 × 9.
Try 3. Since 18 ÷ 3 = 6, write 3 × 6.
Keep trying whole numbers until you reach 6, which is already in your list. Every factor is now found, so you are done.

Prime Factorization of 18

Prime factors show what 18 is built from. Split it and keep going until every branch is a prime.

Handwritten factor tree of 18 splitting down to the circled primes 2, 3 and 3, with 18 = 2 × 3 × 3 = 2 × 3² written below — Factor tree of 18. The circled primes are 2, 3 and 3.

So 18 = 2 × 3 × 3 = 2 × 3². Its prime factors are 2 and 3. Add 1 to each exponent and multiply: (1 + 1) × (2 + 1) = 6, which matches the list.

Divisibility check for 18

A number divides by 18 when it divides by 2 and 9. Take 126: it is even and its digits add up to 9, so 126 is a multiple of 18.

Is 18 a Prime or Composite Number?

Composite. It has six factors. The sum of all factors is 1 + 2 + 3 + 6 + 9 + 18 = 39. The factors smaller than 18 add up to 21, which is more than 18, so 18 is called an abundant number.

Real-Life Uses of the Factors of 18

Golf. A round of 18 holes splits into 2 nines or 3 sixes.
Sharing. Eighteen cookies share evenly between 2, 3, 6 or 9 friends.
Teams. Eighteen players make 3 teams of 6 or 2 teams of 9.

Common Factors of 18 With Other Numbers

The factors of 24 are 1, 2, 3, 4, 6, 8, 12 and 24, so 18 and 24 share 1, 2, 3 and 6. The GCF is 6, which simplifies 18/24 to 3/4.

Quick Practice

Which of these are factors of 18: 5, 6 or 8? Only 6. Now try 21 and check it with the calculator.

Factors of 18