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.
['T', 'n', '8513', '5565', '6343', '1403', '975', '6959', '8049', '1601', 'j', 'Q', 'O', '7889', 'r', 'D', '1903', '6607']