Is 21 a Prime Number? Find Out Instantly!
21 is not a prime number.
What Does It Mean for 21 to Be Prime?
Prime numbers are natural numbers greater than 1 with only two positive divisors: 1 and themselves. If 21 cannot be divided evenly by any other number, it is prime.
How to Check If 21 Is Prime
We test divisibility by all integers from 2 up to the square root of 21. If 21 is divisible by any of those numbers, it is not prime.
Why is 21 Not Prime?
- 21 is divisible by 3 because 21 ÷ 3 = 7
Prime Numbers Less Than 21
Frequently Asked Questions About Prime Numbers
-
What is the smallest prime number?
The smallest prime number is 2.
-
Are even numbers prime?
Only 2 is an even prime number; all other even numbers are composite.
-
What are twin primes?
Twin primes are pairs of primes that differ by 2, such as (11, 13) or (17, 19).
Try Checking Other Numbers
| Number | Prime Status |
|---|---|
| 364 | Not Prime |
| 65 | Not Prime |
| 107 | Prime |
| 264 | Not Prime |
| 144 | Not Prime |
| 21 | Not Prime |
| 176 | Not Prime |
| 44 | Not Prime |
| 19 | Prime |
| 288 | Not Prime |