One thing I was taught as a youngster (a younger youngster) by my mother, was how to keep important numbers hidden in plain sight.
Grab a contacts book, the kind you keep phone numbers and addresses written in. Make up a name that can be either related to what the number is, or just completely random, and make up a phone number using the important number you want to keep hidden.
So for a safe combination of say, 11-12-13 or whatever, you could do this,
Just an idea. I've never really had to use this, as I prefer safes with a key, and can generally remember important numbers.
Imagine what I would do, if I could do all I can.