We live in a world of numbers, are surrounded by them. They play a part in our lives, history, beliefs, myths, taboos and even curses. To greet someone by nodding four times; to use three names, one of them secret, against the evil eye; to place the tips of all five fingers on one’s chest as a sign of sincerity are only some of the superstitions, taboos and habits commonly associated with the power of numbers. But there’s more: we believe the number 13 will affect our lives, giving us good or bad luck depending on which hemisphere we come from. There are dozens of buildings and theatres without a 13th floor or a 13th row. Beliefs about the bad luck of having 13 people sitting at one table and the absence of F13 on the keyboards of computers are only some of the expressions of this numerical fear. How did it start, and based on what? Why are some numbers so relevant? Do numerical taboos make sense?