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.
['A', '5773', '4015', 'D', 'z', '611', '7549', 'w', 'r', '7491', '2727', 'O', 'P', 'j', '4199', '8615', '1985', '3623']