Do you have the perfect brain? Now you do!
Just take out a deck of cards and a pen. Let them shuffle the cards. Then have them call out random digits and proceed to write them on the backs of the cards until you have marked about 30 or 40 cards (or even the whole deck). Fan the cards in front of you for only 5-10 seconds to remember the sequence. Hand the cards to the spectator who called out the final number. You are ready to go: