sudoku 20 min 2.5 - SERP Analysis

https://www.reddit.com/r/sudoku/comments/nlgcy5/whats_the_average_time_you_guys_need_to_finish_an/

https://www.nytimes.com/puzzles/sudoku

https://www.youtube.com/watch%3Fv%3D_QI6xkZnLDQ

https://sudoku.com/extreme/

https://apps.apple.com/us/app/sudoku-com-number-games/id1193508329

https://www.menneske.no/sudoku/nobox/7/eng/

https://www.youtube.com/watch%3Fv%3DsxfDdYvY0Kg

https://www.gmpuzzles.com/blog/category/sudoku/just-one-cell-sudoku/

http://forum.enjoysudoku.com/the-hardest-sudokus-new-thread-t6539-870.html