GCF (HCF) of 5 and 21

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Greatest Common Factor of
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What is the Greatest Common Divisor of 5 and 21?

Answer

GCF (HCF) of 5 and 21 is
1

Common factors: 1

Only 1 divides both: 5 and 21 share no prime factor.

Such numbers are called coprime (relatively prime); their LCM is just the product: 5 × 21 = 105.

5 — prime

21 = 3 × 7

Prime521Lowest power
3—3—
55——
7—7—

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

GCF = 1

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GCF Table

Number 1Number 2GCF
561
571
581
591
5105
5111
5121
5131
5141
5155
5161
5171
5181
5191
5205
5211
5221
5231
5241
5255
5271
5281
5305
5311
5331
5355
5361
5371
5405
5441

FAQ

What is the Greatest Common Divisor of 5 and 21?

GCF (HCF) of 5 and 21 is 1

How to find the GCF of 5 and 21?

You can find the GCF of 5 and 21 by listing all factors of both numbers and picking the greatest common one, or by prime factorization. The GCF of 5 and 21 is 1.

What prime factors do 5 and 21 share?

5 and 21 have no prime factor in common, so the only integer that divides both of them is 1 and their GCF is 1.

How does the GCF reduce the fraction 5/21?

Divide the numerator and the denominator by the GCF 1: 5 ÷ 1 = 5 and 21 ÷ 1 = 21. So 5/21 in lowest terms is 5/21.

Are 5 and 21 coprime?

Yes, 5 and 21 are coprime (relatively prime) because their Greatest Common Factor is 1.

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