Factors of 21
The factors of 21 are 1, 3, 7, 21. It has 4 factors.
Factors of 21
Pick any whole number from 1 to 10,000.
How to work it out
- 1
A factor of 21 is a whole number that divides it with nothing left over. You only need to test the numbers up to ā21 ā 4.58; every one that divides gives a pair.
- 2
The factor pairs are listed in the table below. Together they give 4 factors.
- 3
Prime factorisation: keep dividing by the smallest prime that fits.
- 4
Add all the factors: 1 + 3 + 7 + 21 = 32. Without 21 itself that is 11, so 21 is a deficient number.
LaTeX source of the formulas on this page
\[ 21 = 3 \times 7 \]
Factor pairs of 21
| Factor | Pairs with | Product |
|---|---|---|
| 1 | 21 | 1 Ć 21 = 21 |
| 3 | 7 | 3 Ć 7 = 21 |
Questions
What are the factors of 21?
The factors of 21 are 1, 3, 7, 21. It has 4 factors.
What are the prime factors of 21?
3, 7. As a product: 3 Ć 7.
How many factors does 21 have?
21 has 4 factors (2 factor pairs).
What is the sum of the factors of 21?
32.
Is 21 a prime number?
No. It is divisible by 3, so 21 = 3 Ć 7.