Yesterday evening I had the opportunity of watching this wonderful effect: the magicians ask few spectators to say a number form 1 to 50. All the freely selected numbers are written on a board and they are always in full view. The magician asks one of the spectators to pick a receipt that was in a book on a table. On the receipt there were all the numbers freely chosen. I don't know if this kind of effect sound familiar with you? It was so amazing!! Any suggestion?