Is 81 a prime number?
No, 81 is not a prime number. It is divisible by 3: 81 = 3 × 27.
Is 81 prime?
Pick any whole number from 1 to 10,000.
How to work it out
- 1
A prime number has exactly two factors: 1 and itself.
- 2
It is enough to test the primes up to √81 ≈ 9.00. If none of them divides 81, it is prime.
- 3
3 divides 81 exactly, so it is not prime. Its prime factorisation is
LaTeX source of the formulas on this page
\[ 81 = 3^{4} \]Testing 81 by the primes up to its square root
| Prime | Division | Result |
|---|---|---|
| 2 | 81 ÷ 2 | leaves 1 |
| 3 | 81 ÷ 3 | divides exactly (27) |
| 5 | 81 ÷ 5 | leaves 1 |
| 7 | 81 ÷ 7 | leaves 4 |
Questions
Is 81 a prime number?
No, 81 is not a prime number. It is divisible by 3: 81 = 3 × 27.
What is the next prime after 81?
83.
What is the prime number before 81?
79.
What are the factors of 81?
1, 3, 9, 27, 81.