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', 'E', '7701', 'S', 'c', '1531', '3951', '9405', 'N', '3015', 'H', 'S', 'o', '2183', '8205', 'b', 'P', '8645', 'a']