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.
['3469', 'P', '5883', '3911', '9399', 'i', 'F', 'a', '2577', 'i', 'g', 'O', '2717', 'c', '9937', 'l', '1681', 'f']