What is a Prime Number?
A prime number is a natural number greater than 1 that has no positive divisors other than 1 and itself. Examples: 2, 3, 5, 7, 11, 13…
A number N is prime if it is not divisible by any integer from 2 to √N
First 20 Prime Numbers
| # | Prime | # | Prime | # | Prime | # | Prime |
|---|---|---|---|---|---|---|---|
| 1 | 2 | 6 | 13 | 11 | 31 | 16 | 53 |
| 2 | 3 | 7 | 17 | 12 | 37 | 17 | 59 |
| 3 | 5 | 8 | 19 | 13 | 41 | 18 | 61 |
| 4 | 7 | 9 | 23 | 14 | 43 | 19 | 67 |
| 5 | 11 | 10 | 29 | 15 | 47 | 20 | 71 |
Frequently Asked Questions
Is 1 a prime number?
No. By definition, primes must be greater than 1 and have exactly two distinct divisors. The number 1 has only one divisor (itself), so it is neither prime nor composite.
Is 2 the only even prime?
Yes. Every other even number is divisible by 2, giving it at least three divisors, so 2 is the only even prime number.
How do I find primes quickly?
The Sieve of Eratosthenes is the classic algorithm — list all numbers up to N, then cross out multiples of each prime starting from 2. What remains are all primes up to N.