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.
['F', 'a', 'M', '4611', 'F', 'w', '7717', '7787', 'd', '5439', '1423', '5667', 'O', 'h', 'R', '3025', '2101', 'n', '863']