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.
['S', 'D', '3101', '4967', '8197', '5025', '4257', 'S', 'X', '7641', 'n', '6775', '4719', 'o', '2821', 'x', '5605', '2181']