Microsoft Sudoku

While completing puzzle, you can use your mouse or finger (on a touch screen) to write in the number instead of clicking or using the number pad to get the 50 stylus numbers. There is an option in the menu (right click while in game) and make sure stylus use is turned on. If you want to ignore the feature you will easily get 500 numbers through natural game play.

Start an expert game and use the arrows to go side to side while mashing the number pad. You will get it mid game in no time.

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.