No, that’s not a typo. The numbers you see in the headline for this article are the first four numbers of the magical, mystical, and truly weird Fibonacci sequence. Here’s how it works.

Every number in the sequence is the sum of the previous two numbers. You have to start somewhere – and one is a great place to start anything, right? There’s nothing before one except zero, so if you add zero plus one you get one again. That’s why the first two numbers are both one. (Zero is mathematically a part of the equation, but most of the time you will see the sequence starting with one.)