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.
['1635', 'J', '3477', '8407', 'O', '1177', '1597', '1537', 'o', 'j', 'O', 'T', 'Q', '421', '8841', 'R', '6707', '6237']