input: Write a python function to check whether the given number is co-prime or not.
  assert is_coprime(17,13) == True
  assert is_coprime(15,21) == False
  assert is_coprime(25,45) == False
  
output: def is_coprime(a, b):
      def gcd(x, y):
          while y != 0:
              x, y = y, x % y
          return x
      return gcd(a, b) == 1