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: ['1243', 'L', 'F', 'Z', 'C', 'p', 'l', '3159', 'l', 'z', '3817', 'Q', '991', 'J', 'U', 'T', '3915', '6913', 'S']

1243, 12, 6, 26, 3, 16, 12, 3159, 12, 26, 3817, 17, 991, 10, 21, 20, 3915, 6913, 19