# I forgot my PuzzlingCard PIN

Oh guys... I'm in front of an ATM and want to withdraw some money, but I forgot my 4 digit PIN. Can somebody help me out?

I have a backup card with 6x6 fields, each field has exactly one character!

    - A B C D -
A - 1 1 3 G
B 9 - 1 2 C
C 9 1 - 1 D
D 9 3 6 - -
- L C M - -


How do I have to use it?

• I think you have a digit typo in the code box. – Nautilus Mar 7 '16 at 3:18
• No digit typo - I checked it many times. But your question leads to 2 points: 1. You are on the right way! 2. The text is important! – Varon Mar 7 '16 at 8:58
• @Varon Ah, so you actually do know the answer! No more money troubles for you :p – nine9 Mar 7 '16 at 11:11
• @nine9: I repeated what a passerby said to me. Bad excuse.. I know ;) – Varon Mar 7 '16 at 11:15
• @Varon Make sure to change your pin though! – Bojidar Marinov Mar 7 '16 at 13:18

- The table lists the four digits (called $A,B,C,D$).
- The upper right triangle lists the digit sums of the greatest common divisors; for instance, the greatest common divisor of $B=4$ and $D=6$ equals $2$.
- The lower left triangle lists the least common multiples modulo $9$; for instance, the least common multiple of $B=4$ and $D=6$ is $12$, which yields $3$ when taken modulo $9$; similarly, the least common multiple of $C=7$ and $D=6$ modulo $9$ yields $6$.