GCF (HCF) of 7 and 21

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Greatest Common Factor of
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What is the Greatest Common Divisor of 7 and 21?

Answer

GCF (HCF) of 7 and 21 is
7

Common factors: 1, 7

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

7 — prime

21 = 3 × 7

Prime721Lowest power
3—3—
7777

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

GCF = 7

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GCF Table

Number 1Number 2GCF
741
751
781
791
7101
7111
7121
7131
7147
7151
7161
7171
7181
7191
7201
7217
7241
7251
7287
7301
7357
7361
7427
7431
7461
7497
7511
7567
7637
71057

FAQ

What is the Greatest Common Divisor of 7 and 21?

GCF (HCF) of 7 and 21 is 7

How to find the GCF of 7 and 21?

You can find the GCF of 7 and 21 by listing all factors of both numbers and picking the greatest common one, or by prime factorization. The GCF of 7 and 21 is 7.

What prime factors do 7 and 21 share?

The prime factorizations of 7 and 21 have 7 in common, and multiplying those shared primes gives 7 — exactly the greatest common factor.

How does the GCF reduce the fraction 7/21?

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

See Also