Seems a bit unfair that only either the smallest numbers or the numbers with lots of divisors get their own door sprites. I mean, you can't give sprites to every single number, there are too many. but on the other hand, it's nice to be remembered.

You could probably add more locks onto a 2x2 door, but I think this is the extent of "comfortable" fitting keyholes. Go to 2x3 size.

Also, 24 doors would be more readable as four 6-lock flowers.

For reference, this image is probably the maximum amount of keyholes you can cram onto a 2x2 lock. You really shouldn't use this graphic for twenty locks. Go to thirteen, then if you want more, make the lock larger.

I really like those 9, 11, and 13 lock doors. I also confuse the 12 lock door for 16 locks a lot (not sure why), so I might try making my own version of it.