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: ['6521', 'f', 'm', '1051', 'w', 'C', 'H', 'X', '7715', '5243', '3365', 'l', 'X', 'J', 'y', 'U', '4367', 'v', '8399', '1731', 'z']

6521, 6, 13, 1051, 23, 3, 8, 24, 7715, 5243, 3365, 12, 24, 10, 25, 21, 4367, 22, 8399, 1731, 26