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.
['5209', 'O', 'i', 'U', 'O', '1361', '6569', '6017', '1519', 'E', 'p', '1157', 'J', 'D', 'U', 'F', '7991', 'Z', '5905', 'g']