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.
['6713', 'C', '6989', '3977', 'i', 'A', '6343', 'I', '8133', '5827', 'o', 'N', 'K', 'j', '8581', '687', 'I', '6529', '6595', 'Z']