One of my favorite magic tricks is one I've learnt. You have 31 cards prepared in an order determined by a linear shift register. The audience is allowed to cut

One of my favorite magic tricks is one I've learnt. You have 31 cards prepared in an order determined by a linear shift register. The audience is allowed to cut the deck as often as they want (thus maintaining cyclic order) after which they draw 5 cards. Simply by asking which audience members hold red cards you can compute which cards they're holding. I've also performed this trick by combining two decks with different patterns on the back, allowing you to 'divine' their cards without ever asking a question. See here for details: https://golem.ph.utexas.edu/category/2015/01/mathematics_and_magic_the_de_b.html https://golem.ph.utexas.edu/category/2015/01/mathematics_and...