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.
['151', '2415', 'a', '8651', '2583', 'H', '3591', '1643', 'u', 'h', 'c', 'U', '1661', '5529', 'z', '1443', 'k', '4867']