A prime number is a number which has only  two factors. that is 1 and the number itself.
All these prime numbers are odd numbers except 2. For example 1,2,3,5,7,11,13,....etc1., 1 is a unique no. 2 is the only even prime number.
1 3 1
A prime number can be divided evenly only by 1, or itself. 
And it must be a whole number greater than 1.
Example: 5 can only be divided evenly by 1 or 5, so it is a prime number.
But 6 can be divided evenly by 1, 2, 3 and 6 so it is NOT a prime number (it is a composite number).

Examples: ·  
Is 8 a prime number? No, because it can be divided evenly by 2 or 4 (2×4=8), as well as by 1 and 8.
·         Is 73 a Prime Number? Yes, it can only be divided evenly by 1 and 73.