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: ['B', 'U', 'a', 'O', '3871', '2755', 'U', '9265', 'C', '9051', '5091', '6971', 'g']

2, 21, 1, 15, 3871, 2755, 21, 9265, 3, 9051, 5091, 6971, 7