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.
['j', 'H', 'y', '2659', 'J', 'T', '193', 'F', 'O', 'D', '4829', 'Y', 'G', '2917', 'E', 't', '1973', 'n', 'J', 'n']