input: Write a function called `prime_numbers` that takes two integers as input and returns a dictionary containing all the prime numbers between the two input integers as keys and their respective values. If there are no prime numbers between the two integers, return an empty dictionary.
  assert prime_numbers(8, 20)=={11: 11, 13: 13, 17: 17, 19: 19}
  assert prime_numbers(2, 7)=={2: 2, 3: 3, 5: 5, 7: 7}
  assert prime_numbers(14, 16)=={}
  assert prime_numbers(1, 5)=={2: 2, 3: 3, 5: 5}
  assert prime_numbers(25, 28)=={}
output: def prime_numbers(a, b):
      def is_prime(n):
          if n <= 1:
              return False
          for i in range(2, int(n**0.5) + 1):
              if n % i == 0:
                  return False
          return True
      
      primes = {}
      for num in range(a, b + 1):
          if is_prime(num):
              primes[num] = num
      return primes