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.
['1685', 'c', 'K', 'T', 'D', 'A', 'k', 'O', '1273', '99', '3581', '5353', '8715', 'S', '8917', 'P', '6447', 'O', 'X', 'Z']