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.
['C', '9973', 'b', '693', 'y', 'H', 'C', 'P', 'b', 'J', 'f', 'T', '2317', 'O', '5755', '8201', 'p', 'y', '8721', 'i']