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.
['B', 'w', '4423', 'G', '4073', 'D', 'm', '9381', '47', '2783', 'C', '1157', 'u', '453', '447', '9623', 'O', '251', 'i', 'J']