@edstock,
there are 15 letters but only 12 unique numbers.
starting with A = 1 doesn't look promising
A O C P D R F S H T I U J W L
1 2 3 4 5 6 7 8 10 11 12 13
A b c d e f g h i j k l m n o p q r s t u v w x y z
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26