Let’s observe the factors of few natural numbers.
We can see that number 1 has only one factor (i.e. itself).There are numbers that have exactly two factors i.e.1 and the number itself. Such numbers are 2, 3, 5, etc. These numbers are prime numbers. A number is called prime when it can't be divided evenly by any number except 1 or itself.
Example: 19
19 have only two factors, 1 and 19. 19 cannot be divided evenly by numbers other than 1 or itself. So, 19 is a prime number.
Example: 6 and 35 are co-prime
Let’s observe factors of natural numbers again.
There are numbers having more than two factors like 4, 6, etc. These numbers are composite numbers. When a number can be divided up evenly it is a Composite Number. A composite number has factors in addition to one and itself.
Example: 15
15 have three factors, 1, 5 and 15. 15 can be divided evenly by numbers other than 1 or itself. So, 15 is a composite number.
Important Notes: