Numbers are really strange. Human beings are fascinated by them. They are everywhere; in the time, the date, our age, the number (and postcode) at which we live, the amounts other people value us enough to pay us, on the face of our phone, the number of marriages we have behind (but curiously, never before) us. The ones on our driving licences and passports, and that really odd National Insurance Number, identify us, as do the number of teeth that failed to be knocked out in a plane crash in which we were sitting between seats 33 and 51.