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.
['o', 'X', '8427', 'u', 'Z', 'r', '7827', 'L', '4347', '1503', '5961', 'H', 'M', 'g', 'a', '6923', '8407', '4565']