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.
['j', '5647', '9731', '6395', '177', '7621', 'k', '8285', 'F', 'N', 'I', '1571', 'J', 'J', 'P', '3627', '2793', '7413', 'z']