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.
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