input: Write a python function to classify numbers as divisible by 3 and print the results.
  assert classify_numbers([1, 3, 6, 7, 9]) == None
  assert classify_numbers([10, 20, 30]) == None
  assert classify_numbers([0, 9, 18, 21]) == None
output: def classify_numbers(numbers):
      divisible_by_3 = [num for num in numbers if num % 3 == 0]
      not_divisible_by_3 = [num for num in numbers if num % 3 != 0]
      print("Divisible by 3:", divisible_by_3)
      print("Not divisible by 3:", not_divisible_by_3)