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: ['U', 'r', '6121', '8823', 't', '6815', 'l', 'D', '2421', 'G', '7877', 'i', 'B', '781', 'c', 'A', '4021', '8813']

21, 18, 6121, 8823, 20, 6815, 12, 4, 2421, 7, 7877, 9, 2, 781, 3, 1, 4021, 8813