In this task, you are given an input list A. You need to find all the elements of the list that are numbers and calculate their sum.
['8391', '8531', '5267', 'v', '6691', 'N', 'F', 'F', 'O', 'S', 'a', 'G', '8401', '7617', 'C', '8345', 'c', '767']