GCF (HCF) of 21 and 42

"Greatest Common Factor" Calculator
Greatest Common Factor of
and

What is the Greatest Common Divisor of 21 and 42?

Answer

GCF (HCF) of 21 and 42 is
21

Common factors: 1, 3, 7, 21

21 divides 42 (42 ÷ 21 = 2), so the GCF is the smaller number itself.

21 = 3 × 7

42 = 2 × 3 × 7

Prime2142Lowest power
2—2—
3333
7777

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

GCF = 3 × 7 = 21

More with these numbers

Related Calculations

See Also

GCF Table

Number 1Number 2GCF
21221
21243
21251
21261
21273
21287
21303
21321
21333
21357
21363
21371
21381
21393
21401
214221
21441
21453
21461
21483
21497
21501
21513
21543
21567
21603
21693
21801
218421
2110521

FAQ

What is the Greatest Common Divisor of 21 and 42?

GCF (HCF) of 21 and 42 is 21

How to find the GCF of 21 and 42?

You can find the GCF of 21 and 42 by listing all factors of both numbers and picking the greatest common one, or by prime factorization. The GCF of 21 and 42 is 21.

What prime factors do 21 and 42 share?

The prime factorizations of 21 and 42 have 3 × 7 in common, and multiplying those shared primes gives 21 — exactly the greatest common factor.

How does the GCF reduce the fraction 21/42?

Divide the numerator and the denominator by the GCF 21: 21 ÷ 21 = 1 and 42 ÷ 21 = 2. So 21/42 in lowest terms is 1/2.

See Also