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.
['3657', 'b', 'b', '5007', '6537', 'q', 'y', 'c', 'U', 'N', '3657', '3111', '2849', 'a', '905', 'T', '8145', 't', '3577', '1791']