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Factors of 21

"Factors of a Number" Calculator

What are the Factors of 21?

Answer

Factors of 21:

1, 3, 7, 21

4 factors · 21 = 3 × 7 · composite

Underlined — prime: 3, 7 · 1 — neither prime nor composite · others — composite

Factor pairs of 21

2 pairs: 1 × 21 · 3 × 7

Past √21 ≈ 4.58 every pair would repeat one already found — so checking stops at 4.

21 = 3 × 7 → (1 + 1) × (1 + 1) = 4 factors: add 1 to each exponent and multiply.

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See Also

Prime Number Checker - Find out whether a given number is Prime or not
Prime Factorization - Prime Factorization Calculator
Prime Numbers List - List of all Prime Numbers - how many Prime numbers are between

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Factors of 21. Factors of 21: full list and factor pairs.

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Factors Table

Number	Factors
6	1, 2, 3, 6
7	1, 7
8	1, 2, 4, 8
9	1, 3, 9
10	1, 2, 5, 10
11	1, 11
12	1, 2, 3, 4, 6, 12
13	1, 13
14	1, 2, 7, 14
15	1, 3, 5, 15
16	1, 2, 4, 8, 16
17	1, 17
18	1, 2, 3, 6, 9, 18
19	1, 19
20	1, 2, 4, 5, 10, 20
21	1, 3, 7, 21
22	1, 2, 11, 22
23	1, 23
24	1, 2, 3, 4, 6, 8, 12, 24
25	1, 5, 25
26	1, 2, 13, 26
27	1, 3, 9, 27
28	1, 2, 4, 7, 14, 28
29	1, 29
30	1, 2, 3, 5, 6, 10, 15, 30
31	1, 31
32	1, 2, 4, 8, 16, 32
33	1, 3, 11, 33
34	1, 2, 17, 34
35	1, 5, 7, 35

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FAQ

What are the Factors of 21?

Factors of 21: 1, 3, 7, 21

How many factors does 21 have?

Number 21 has 4 factors

How many Factor Pairs does 21 have?

Number 21 has 2 factor pairs

Is 21 a prime or composite number?

Composite: 21 = 3 × 7, so it has 4 factors — a prime has exactly two.

How many factors does 21 have excluding 1 and 21?

2: 3 and 7.