The number which has only one factor is 

Every number is multiple of 

Two numbers having only 1 as a common factor are called 

Natural numbers which are exactly divisible by 2 are called 

The numbers whose units digit is 0, 2, 4, 6 or 8 are called 

Even numbers can be represented as

Natural numbers which are not divisible by 2 are called 

Odd numbers can be represented as

The sum of first 'n' odd natural numbers is

The sum of first 'n' even natural numbers is