Check Prime Number Function

Write a function is_prime(n) : It tests if n is a prime number (True) or not (False). 

Examples

is_prime(15) ➞ False
is_prime(31) ➞ True
is_prime(1) ➞ False

Note: 

• Writing a function is compulsory for this problem. Use "is_prime" as a function name.
  
• Don't forget to return the result.