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GCF (HCF) of 45 and 81

"Greatest Common Factor" Calculator

What is the Greatest Common Divisor of 45 and 81?

Answer

GCF (HCF) of 45 and 81 is

9

Common factors: 1, 3, 9

9 divides both: 45 ÷ 9 = 5, 81 ÷ 9 = 9 — and 5 and 9 share no factor but 1, so no larger number divides both.

45 = 3² × 5

81 = 3⁴

Prime	45	81	Lowest power
3	3²	3⁴	3²
5	5	—	—

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

GCF = 3² = 9

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See Also

Least Common Multiple - Find the Least Common Multiple (LCM) of two numbers
Greatest Common Factor of 3 Numbers - Find the Greatest Common Factor (GCF) of three numbers
Least Common Multiple of 3 Numbers - Find the Least Common Multiple (LCM) of three numbers

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What is the GCF (HCF) of 45 and 81. The GCF of 45 and 81 is 9 — the biggest number that can divide both integers. Step-by-step GCF (GCD) calculation by factoring.

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GCF Table

Number 1	Number 2	GCF
45	48	3
45	49	1
45	50	5
45	51	3
45	52	1
45	54	9
45	55	5
45	56	1
45	60	15
45	63	9
45	65	5
45	70	5
45	72	9
45	75	15
45	76	1
45	80	5
45	81	9
45	90	45
45	95	5
45	99	9
45	100	5
45	105	15
45	108	9
45	117	9
45	120	15
45	125	5
45	135	45
45	150	15
45	180	45
45	405	45

FAQ

What is the Greatest Common Divisor of 45 and 81?

GCF (HCF) of 45 and 81 is 9

How to find the GCF of 45 and 81?

You can find the GCF of 45 and 81 by listing all factors of both numbers and picking the greatest common one, or by prime factorization. The GCF of 45 and 81 is 9.

What prime factors do 45 and 81 share?

The prime factorizations of 45 and 81 have 3 × 3 in common, and multiplying those shared primes gives 9 — exactly the greatest common factor.

How does the GCF reduce the fraction 45/81?

Divide the numerator and the denominator by the GCF 9: 45 ÷ 9 = 5 and 81 ÷ 9 = 9. So 45/81 in lowest terms is 5/9.