Types of Numbers
(a)     Even Number : A number which is exactly divisible by 2 is called an even number.
Examples of even numbers are : 0, 12, 34, 56, 78,....

(b)     Odd Number : A number which is not exactly divisible by 2 is called an odd number.
Examples of odd numbers are : 1, 13, 15, 25, 29,....

(c)     Prime Numbers : A natural number greater than 1, which has no factors except 1 and itself is called a prime number.
Examples of prime numbers are : 2, 3, 5, 11, 13, 17, ...

(d)     Composite Numbers : A number is composite if it has at least one factor other than 1 and itself.
Examples of composite numbers are : 4, 6, 8, 9,10, 12, 14,...
Note :
(i)     1 is neither prime nor composite.
(ii)     Every natural number except 1 is, either a prime number or a composite number.
(iii)     2 is the only prime number which is even. All other prime numbers are odd.

(f)     Perfect Numbers : If the sum of all the factors of a number is twice the number, then number is called a perfect number. For example, 6 is a perfect number since the factors of 6 are 1, 2,3, 6 and their sum 1 + 2 + 3 + 6 = 2 × 6.

(g)     Coprime Numbers : Two numbers are said to be coprime if they do not have a common factor other than 1.
Examples of coprime numbers are : (8, 15); (5, 9); (2, 11)

Note :
(i)    Two prime numbers are always coprime.
(ii)     Two coprime numbers need not be both prime numbers.