GCF (HCF) of 3 and 21

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Greatest Common Factor of
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What is the Greatest Common Divisor of 3 and 21?

Answer

GCF (HCF) of 3 and 21 is
3

Common factors: 1, 3

3 divides 21 (21 ÷ 3 = 7), so the GCF is the smaller number itself.

3 — prime

21 = 3 × 7

Prime321Lowest power
3333
7—7—

— = power 0: the prime is not a factor of this number, so it cannot be in the GCF.

GCF = 3

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GCF Table

Number 1Number 2GCF
341
351
363
371
381
393
3101
3111
3123
3141
3153
3161
3171
3183
3191
3213
3221
3243
3251
3273
3303
3341
3363
3423
3453
3461
3471
3483
3513
3543

FAQ

What is the Greatest Common Divisor of 3 and 21?

GCF (HCF) of 3 and 21 is 3

How to find the GCF of 3 and 21?

You can find the GCF of 3 and 21 by listing all factors of both numbers and picking the greatest common one, or by prime factorization. The GCF of 3 and 21 is 3.

What prime factors do 3 and 21 share?

The prime factorizations of 3 and 21 have 3 in common, and multiplying those shared primes gives 3 — exactly the greatest common factor.

How does the GCF reduce the fraction 3/21?

Divide the numerator and the denominator by the GCF 3: 3 ÷ 3 = 1 and 21 ÷ 3 = 7. So 3/21 in lowest terms is 1/7.

See Also