Definition: In this task, you are given an input list A. You need to convert all the alphabets in the list with a number representing their position in the English alphabet. E.g., replace A by 1, B by 2, a by 1, b by 2, and so on.
Input: ['O', '6347', '7875', '5637', 'b', '2857', '1429', '2687', '8449', 'X', '4771', 'G', '1399']

15, 6347, 7875, 5637, 2, 2857, 1429, 2687, 8449, 24, 4771, 7, 1399