Factors of 18
There are 6 factors of 18 — the full list is below, with factor pairs, prime factorization, and divisibility notes.
Factors of 18
1, 2, 3, 6, 9, 18
Factor pairs of 18
- 1 × 18
- 2 × 9
- 3 × 6
Prime factorization of 18
18 = 2 × 3²
Number facts
- 18 is a composite number.
- 18 has 6 factors.
- 18 is not a perfect square.
- The sum of all factors of 18 is 39.
Divisibility rules that apply to 18
- 18 is divisible by 2 because it ends in an even digit (0, 2, 4, 6, or 8).
- 18 is divisible by 3 because the sum of its digits (9) is divisible by 3.
- 18 is divisible by 9 because the sum of its digits (9) is divisible by 9.
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How the factors of 18 are calculated
To find the factors of 18, every whole number from 1 up to the square root of 18(about 4.24) is tested for even division. 18 is even, and it divides evenly by 2, 3, 6, 9. Written as a product of primes, 18 = 2 × 3², which confirms every factor above is a combination of those prime building blocks.
Frequently asked questions about 18
How many factors does 18 have?
18 has 6 factors: 1, 2, 3, 6, 9, 18.
Is 18 a prime number?
No. 18 is composite because it has factors other than 1 and itself.
What are the factor pairs of 18?
The factor pairs of 18 are 1 × 18, 2 × 9, 3 × 6.
What is the prime factorization of 18?
The prime factorization of 18 is 2 × 3².