Is 81 Prime?

Check if 81 is a prime number. A prime number is only divisible by 1 and itself.

Result: ✗ NO — 81 is NOT a prime number

Step-by-Step Solution

Step 1 What is a Prime Number?

A prime number is a natural number greater than 1 that has exactly two factors: 1 and itself.

To check if 81 is prime, we need to verify that no number from 2 to √81 divides it evenly.

Step 2 Determine Testing Range

Since 81 is odd, we only need to check odd divisors.

We only need to test up to √81 ≈ 9.00, which rounds down to 9.

If 81 has a factor larger than √81, it must also have a corresponding factor smaller than √81.

Step 3 Test Odd Divisors

Testing: 3, 5, 7, ... up to 9

81 ÷ 3 = 27 (no remainder!)

We found that 3 divides 81 evenly!

Step 4 Conclusion

81 = 3 × 27

Since 81 has factors other than 1 and itself, 81 is NOT a prime number.