The factors of 21 are 1, 3, 7 and 21. That is 4 factors in total.
A factor of 21 is a whole number that divides 21 exactly, with no remainder. 21 is a composite number because it has factors other than 1 and itself.
Two numbers that multiply to give 21:
21 = 3 × 7. The prime factors of 21 are 3 and 7.
| Number | Factors |
|---|---|
| 17 | 1, 17 |
| 18 | 1, 2, 3, 6, 9, 18 |
| 19 | 1, 19 |
| 20 | 1, 2, 4, 5, 10, 20 |
| 22 | 1, 2, 11, 22 |
| 23 | 1, 23 |
| 24 | 1, 2, 3, 4, 6, 8, 12, 24 |
| 25 | 1, 5, 25 |
More about 21: 21 squared · square root of 21 · 21 in binary · 21 in Roman numerals.
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