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.
['1365', 'n', 't', '6353', 'p', 'l', '6403', '6491', 'j', '6511', '8529', '2049', 'o', 'Z', '51', 'p', 'Q', '4751', '5493']