input: from typing import List
  
  def find_common_elements(list1: List[int], list2: List[int]) -> List[int]:
      """
      Find and return the common elements between two given lists of integers.
  
      >>> find_common_elements([3, 9, 15, 21, 27], [21, 7, 13, 29, 31])
      [21]
      """
      common_elements = []
      for i in list1:
          for j in list2:
              if i == j:
                  common_elements.append(i)
      return common_elements
output:     common_elements = []
      for i in list1:
          if i in list2 and i not in common_elements:
              common_elements.append(i)
      return common_elements