21

You really don't get it...

When 1.3.1 was first released, two mapmakers named Baih and Noel made a custom map showcasing what you could do with the new wiring. One part of the map had two doors and some numbers set up to create math problems, and you had to match the numbers to make correct math problems to open the doors. Well, some wiring was wrong and the machine accepted 9 + 1 = 11 to open one of the doors. The YouTuber Pedguin found that out and since he's so popular, all his fans turned that into sort of an inside joke, and apparently the devs liked it enough to make it a title.