input: def prime_numbers_less_than(n):
      """Write a function that accepts a non-negative integer n and returns a list of the prime numbers that are less than n.
      for example:
      prime_numbers_less_than(5) => [2, 3]
      prime_numbers_less_than(11) => [2, 3, 5, 7]
      prime_numbers_less_than(0) => []
      prime_numbers_less_than(20) => [2, 3, 5, 7, 11, 13, 17, 19]
      prime_numbers_less_than(1) => []
      prime_numbers_less_than(18) => [2, 3, 5, 7, 11, 13, 17]
      """
output:     if n <= 2:
          return []
      primes = []
      for num in range(2, n):
          is_prime = True
          for factor in range(2, int(num**0.5) + 1):
              if num % factor == 0:
                  is_prime = False
                  break
          if is_prime:
              primes.append(num)
      return primes