Twelve musical numbers are created due to the fact that the normal single digit (0-9) can only express 10 pitches. Music deserves to have its own numbers to express 12 pitches.
Instead of using 0-9, %, and !, new digits are made so that they look alike with each other. It is easy to learn these new numbers.
An alternative arrangement can be:
The little circle denotes a double duration, which is my own idea.