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.
['H', '9771', 'j', 'J', '2127', 'Y', 't', 'N', '5533', '8763', 'N', '4951', 'L', 'i', 'v', 'r', 'B', 'P']