# Prime Number

What is prime number?

A number which is divisible by only itself and 1 is a prime number. So, prime number has only two different factors normally 1 and the number itself.

A whole number having only 2 factors is called the prime number.

The two factors of a prime number are 1 and the number itself.

Let us find all the factors of 2, 3, 5, 7, 11, 13, 17 and 19.

(i) 2 → the factors are 1 and 2.

1 × 2 = 2

2 × 1 = 2

(ii) 3 → the factors are 1 and 3.

1 × 3 = 3

3 × 1 = 3

(iii) 5 → the factors are 1 and 5.

1 × 5 = 5

5 × 1 = 5

(iv) 7 → the factors are 1 and 7.

1 × 7 = 7

7 × 1 = 7

(v) 11 → the factors are 1 and 11.

1 × 11 = 11

11 × 1 = 11

(vi) 13 → the factors are 1 and 13.

1 × 13 = 13

13 × 1 = 13

(v) 17 → the factors are 1 and 17.

1 × 17 = 17

17 × 1 = 17

(vi) 19 → the factors are 1 and 19.

1 × 19 = 19

19 × 1 = 19

Therefore,

2 is divisible only by 1 and 2. Therefore, the factors of 2 are 1 and 2.

3 is divisible only by 1 and 3. Therefore, the factors of 3 are 1 and 3.

5 is divisible only by 1 and 5. Therefore, the factors of 5 are 1 and 5.

7 is divisible only by 1 and 7. Therefore, the factors of 7 are 1 and 7.

11 is divisible only by 1 and 11. Therefore, the factors of 11 are 1 and 11.

13 is divisible only by 1 and 13. Therefore, the factors of 13 are 1 and 13.

17 is divisible only by 1 and 17. Therefore, the factors of 17 are 1 and 17.

19 is divisible only by 1 and 19. Therefore, the factors of 19 are 1 and 19.

Thus 2, 3, 5, 7, 11, 13, 17 and 19 are prime numbers.

Note:

(i) All prime numbers except 2, are always odd numbers.

(ii) The number 2 is a prime as well as an even number.

(iii) All prime numbers are exactly divisible by 1 and the number itself.