That is a cool pattern. The final multiplication by 7 totally caught me by surprise! Very cool stuff indeed. I bought the book. Now I need to go read it 🙂
Hey, thank you for sharing this. Although I understand how to apply it, I am afraid I did not really get the principle. Should not the fourth card read: 4, 5, 6, 7, 12, 13, 14, 15, …? What did I miss? Thanx.