I think I just came upon a secret reception. I was just about to go in when a guard stopped me and asked for my number. I wasn't sure how the system worked but I was able to see the checklist of attendants. One code number was missing and I used it. Basically the checklist was like this; Do you know what my attendant code is?
Your code was
The three numbers at the top of each box are the codes for the checklist, as shown by your missing numbers replaced with ?s.
Underneath each code is a blank keypad shape with the numbers 1, 2, and 3
These represent the first, second, and third keys pressed on a keypad. The keypad looks like this:
1 2 3
4 5 6
7 8 9
we know the numbers on the keypad from looking at the other attendant codes, 2 is the first number pressed in 249, 5 is the first number pressed in 573, and 8 is the first number pressed in 819.