Factors of 81
There are 5 factors of 81 — the full list is below, with factor pairs, prime factorization, and divisibility notes.
Factors of 81
1, 3, 9, 27, 81
Factor pairs of 81
- 1 × 81
- 3 × 27
- 9 × 9
Prime factorization of 81
81 = 3⁴
Number facts
- 81 is a composite number.
- 81 has 5 factors.
- 81 is a perfect square.
- The sum of all factors of 81 is 121.
Divisibility rules that apply to 81
- 81 is divisible by 3 because the sum of its digits (9) is divisible by 3.
- 81 is divisible by 9 because the sum of its digits (9) is divisible by 9.
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How the factors of 81 are calculated
To find the factors of 81, every whole number from 1 up to the square root of 81(about 9.00) is tested for even division. 81 is odd, and it divides evenly by 3, 9, 27. Written as a product of primes, 81 = 3⁴. 81 is also a perfect square, which is why one of its factor pairs is a number multiplied by itself.
Frequently asked questions about 81
How many factors does 81 have?
81 has 5 factors: 1, 3, 9, 27, 81.
Is 81 a prime number?
No. 81 is composite because it has factors other than 1 and itself.
What are the factor pairs of 81?
The factor pairs of 81 are 1 × 81, 3 × 27, 9 × 9.
What is the prime factorization of 81?
The prime factorization of 81 is 3⁴.