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.
['n', 'O', 'Z', '5333', 'T', 'K', '6421', 'q', '5769', 'b', 'f', 'h', 'r', 'Z', 'd', '9839', 's', '4631', '1903']