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.
['1233', 'n', '7683', '9499', 'o', '7535', 'a', 'D', '1841', '2961', '4189', '431', '2413', 'k', 't', '9755', '3741', 'B', '7401', 'X']