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