Why 1 is not a prime number?

1 is not a prime number nor composite number because it has only its one factor which is 1.

The Prime numbers have 2 factors such as 13 has two factors 1, 13.

The composite numbers have 3 or more than 3 factors like 9 has 1,3,9 as factors and 6has 1,2,3,6 as its factor

Now did you understood why 1 is not a prime number nor composite number.