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.
['R', '1181', '719', 'Y', '3397', '5561', 'q', '5963', '7573', 'T', 'p', '583', 'B', '3909', '4863', '8571', 'n', 'j']