Most of us carry credit cards and ATM cards. These, typically, have sixteen digits on the front. These digits are the unique account number for the card. For obvious reasons, just any sixteen digits ...

Katie has a PhD in maths, specializing in the intersection of dynamical systems and number theory. She reports on topics from maths and history to society and animals. Katie has a PhD in maths, ...

Those 15 or 16 numbers embossed on the front of each of your credit cards aren’t randomly assigned. That sequence of digits has actual meaning and indicates everything from your account information to ...