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.
['T', 'D', '5179', '5777', 'i', '4027', '9613', '3445', 'T', '4999', 'J', '2123', '4563', 'w', '1739', '3881', 'g', '5943']