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: ['F', '3129', 'f', '3491', '7759', '821', '1851', '6409', 'l', 'U', '9741', 'T', 't', 'h', '81', '6469', 'b', 'T', 'I']

6, 3129, 6, 3491, 7759, 821, 1851, 6409, 12, 21, 9741, 20, 20, 8, 81, 6469, 2, 20, 9