While placing 500 Numbers is a grind, it will be the only sure fire way to get this one. If playing Normally, or to get other achievements, You'll need to complete several puzzles to complete this.
To get it via the 50 Stylus method, you'll need to either a tablet or pen stylus compatible device. You'll have this achievement within one or two puzzle completions. It will be worth noting that Windows 10 may need to detect the hardware as a tablet or stylus. I personally used a UGEE 1560 Drawing Display to obtain this. Please not that there is an option in the game to pick enable Stylus input or to disable it.