Magical Mathematics

I perform a four-card trick twice, work out why it cannot fail, and generalize it to bigger decks. The classic 27-card trick comes with variations that are practical to perform, and a trick driven by a fixed function comes with the logic underneath it. De Bruijn sequences, cyclic strings in which every block of a given length appears exactly once, are the idea behind some of the most surprising card tricks, and I explain how they work.