screwdriver head. perelman's "mathematics can be fun" has that and another couple of fun examples https://archive.org/details/MathematicsCanBeFun-Eng-YakovPerel

screwdriver head. perelman's "mathematics can be fun" has that and another couple of fun examples https://archive.org/details/MathematicsCanBeFun-Eng-YakovPerelman/page/n133/mode/2up https://archive.org/details/MathematicsCanBeFun-Eng-YakovPer... i got a copy of that book and gardner's "mathematical magic show" when i was 12 or so, and they both continue to entertain and delight me.