![Can you solve the fortress riddle? - Henri Picciotto](https://i.ytimg.com/vi/s5CLtBaRIwY/sddefault.jpg)
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dinosaurs tiny dinosaurs jurassic park sieve of eratosthenes eratosthenes prime numbers ancient greece nation states siege siege weapons fortress castle walls dinosaur herd castle fortifications wall reinforcements clowns royals redheads wall fabricator riddle ted ed riddles mathematics math education animation Henri Picciotto igor coric artrake studio TED TED-Ed TED Ed Teded Ted Education