Of course Simon Tatham’s puzzle collection includes this one. He calls it “rectangle”. You can configure the game to leave spaces around the numbers, which increases the difficulty. There’s a web based version here:
<a href="https://www.chiark.greenend.org.uk/~sgtatham/puzzles/js/rect.html" rel="nofollow">https://www.chiark.greenend.org.uk/~sgtatham/puzzles/js/rect...</a>
If you like these kind of games, there are millions of them at <a href="https://puzz.link/db/" rel="nofollow">https://puzz.link/db/</a>
#ShikakuOfTheDay
#EASY240413 02:39.21
#MEDIUM240413 04:40.83
#HARD240413 12:20.11
#EXPERT240413 58:44.96
<a href="https://shikakuofthe.day" rel="nofollow">https://shikakuofthe.day</a><p>I imagine master will take a couple of hours to complete, so I didn’t even attempt it.