Hello, everyone! Before Christmas, I showed you some sequences of numbers. They were called de Bruijn sequences. And they’re designed to contain every combination of some numbers without repeating any combinations. For example, this sequence [1111 2222 1221 1212] contains every combination of 1 and 2 of length four. So 1111 is in there. 2212 is in there. And even something like 1211 is in there, but it wraps around–it goes back to the start. So, the inventor of these sequences, Nicolaas de Bruijn, he died in February, I’m afraid. But don’t feel too bad for him– he was 93. But in honor of Nicolaas de Bruijn, I’m going to show you a card trick that uses this sequence. So this is the idea: you get a pack of cards, and these can be cut, as many times as you want, and you can give them to your volunteers, and they can cut them. And then you get four volunteers and they each take a card off the top of the pack. So Volunteer 1, Volunteer 2, Volunteer 3, and Volunteer number 4. So they each pick a card, And you say, “Oh, right. I’m going to read your mind. Ah, but with four of you, it’s a bit difficult. The transmission is not getting through. To clear up the transmission, which ones of you have a red card?” And, hopefully, your volunteers with a red card will give you a little wave. And you’ll go, “Oh, right, that helps. Thank you. I can now name your cards.” And you’ll be able to name each volunteer’s card, and get it right. Now, how does this work? Let’s take a look. We’re going to use this sequence that we saw before, but instead of ones and twos, I’m now going to change this into blacks and reds. So the sequence now looks like this. [BBBB RRRR BRRB BRBR] To make this card trick work, we’re going to have to memorize 16 cards in this order. Now, you’re free to pick your own sequence of 16 cards, but here’s one that I’ve made up. Now, my idea here was to split it into four blocks of 4, to begin each block with ace, two, three and four, and the cards in each block increase by four. So I’ve got ace, five, nine, and king. Then I have two, six, ten and ace. And so on. The suits I’ve tried to keep in CHSD [‘chased’] order. That’s C-H-S-D. Clubs, hearts, spades and diamonds. So the first block of four was clubs-spades-clubs-spades. The last block of four is actually in CHSD order. The third block of four is a bit of a cheat. I’ve started off in CHSD order– clubs and hearts– then I’ve had to do a little switch there so it’s diamonds and spades. Now, if you can memorize this sequence, you can do this trick. I made this sequence four times over, [edit: I meant 3 times over] using four decks of cards, put them together, and you’ll make 4 times 16 lots of cards, [3×16=48] which is 48 cards. So you’ve got a deck of 48 cards. When you cut the pack, that doesn’t affect the sequence at all. And if your volunteers give you a wave, to show you which ones are red, you can use that to identify where in the sequence you are, and you can name their cards. So, for example, you’ve got your four volunteers, and maybe the first, second and fourth volunteer have a red card. Then you’re looking for the sequence RRBR. And if you can use that memorized sequence of 16, you know that they have picked the 10 of Hearts, the Ace of Diamonds, the 3 of Clubs, and the 7 of Hearts. Now, you do have to memorize this sequence. So it’ll take some practice. Or maybe you can use a cheat sheet hidden somewhere. But it can be done, and that’s a challenge to the magicians out there. So over to you! And if you have been, thanks for watching.