Nathaniel, thanks for playing! I found this great typewriter soundpack on Freesound.org and decided to base the game's whole soundscape around it. Originally, I designed the game to be how you imagined it to be, where each number can only be used once. That was way too hard, so I decided to allow numbers to be re-used and wrote a more gentle solver / puzzle generator. Then when I came up with the modifiers, I realized I could use my original solver again for players who wanted a challenge. Always interesting what players can see no matter how I tried to obscure it.