Prime Numbers

Definition

A natural number that has two and only two divisors - 1 and itself, is called a prime number.

For example, the number 2 is a prime number because it has only two divisors - 1 and itself. It cannot be divided by any other number without getting a fractional answer. Thus, 2 is a prime number.

First 10 Prime Numbers

Here is a list of the first 10 prime numbers: 2, 3, 5, 7, 9, 11, 13, 17, 19, 23.

2 Is The Only Even Number That Is Prime

In the list of the first 10 prime numbers given above, you may note that all the numbers are odd - except 2. 2 is the only even number that is prime. Why? The reason is in the definition of even numbers - 

"An even number is a number divisible by 2"

Thus if we consider any even number, say 4, then it will have the factor 2 (other than 1 and itself) and thus it will not be a prime number. On the other hand 2 is an even number because it is divisible by 2 but it is also a prime number since it is only divisible by 1 and itself. Thus 2 is the only even numbers that is prime.

First 100 Prime Numbers

Just for interest, here is a list of the first 100 prime numbers: 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97, 101, 103, 107, 109, 113, 127, 131, 137, 139, 149, 151, 157, 163, 167, 173, 179, 181, 191, 193, 197, 199, 211, 223, 227, 229, 233, 239, 241, 251, 257, 263, 269, 271, 277, 281, 283, 293, 307, 311, 313, 317, 331, 337, 347, 349, 353, 359, 367, 373, 379, 383, 389, 397, 401, 409, 419, 421, 431, 433, 439, 443, 449, 457, 461, 463, 467, 479, 487, 491, 499, 503, 509, 521, 523, 541.

1 Is Not A Prime Number

1 is not a prime number since it does not have two divisors. A number must have two and only two divisors - 1 and the number itself - in order to be prime. This is explained further in this post.

0 Is Not A Prime Number

0 is not a prime number because it can be divided by all numbers. For example, `0/2 = 0` and `0/100 = 0`. 0 has an infinite number of factors/divisors. Thus it is not a prime number.