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.
['4101', 'q', '2007', '473', '5071', 'a', 'O', '5565', '9199', '9535', 'J', 'D', 'O', 'I', '31', '5019', 'L', '2979', 'a']