Use combining characters?

[joakim]

Instead of 20 unique characters, you could have only the first 5 numerals, plus 3 combining characters for the "fives", to compose all 20 numerals. 20 for the price of 8 🎉

That means you could have a keyboard with only 5 number keys (0-4) and use a compose key to write all 20 numerals.

For numerals 0-4, just type the number key directly.
For numerals 5-9, press Compose + 1, then the number key.
For numerals 10-14, press Compose + 2, then the number key.
For numerals 15-19, press Compose + 3, then the number key.

(Edited, thanks to Fuseteam)

Or even better, add a key for the 5 numeral that works sort of like a compose key of combining characters. Press it to compose "fives" that take a numeral (0-4) below it. So pressing the 5 key twice, then pressing 4 gives you the numeral for 14.

[Fuseteam]

that may be easier with a compose key

[joakim]

Had to look it up, but that's what I meant. Mac doesn't have a compose key, which is why I used Shift. But yea, that's what I was thinking of, just didn't know it was called a compose key. Thanks 👍

[Fuseteam]

sure no problem i'm positive you can map the compose key on mac too