*Do you like the number e? Then you might like this curious fact discovered by Aziz Inan of the University of Portland.*

Every year on February 7 maths enthusiasts celebrate *e* day. That's because the first two digits of the number *e* are 2 and 7, and because February 7, written the American way with the month first, is 2/7.

The year 2018 saw a very special *e* day: February 7, 2018 is written as 2/7/18, and 2, 7, 1, and 8 represent the first four digits of *e*. This coincidence occurs only once a century!

But there is more: the calendar date that follows 2/7/18, namely 2/8/18, coincides with the next four digits of *e*. So 2/7/18 and 2/8/18 put side by side as 27182818 constitute the first eight digits of *e*. This property makes the once-a-century special *e* Day 2/7/18 even more special!

*To find out more about the number e and some interesting properties of its digits, see
this article by Aziz Inan. You may also want to
read the following Plus articles.*

Maths in a minute: Compound interest and *e* — Compound interest is the curse of debt and the blessing of saving. Find out how it works and what it has to do with

Maths in a minute: Euler's identity —Here's a quick introduction to the beauty queen amongst mathematical formulas, which involves .

The making of the logarithm —The natural logarithm is intimately related to the number and that's how we learn about it at school. When it was first invented, though, people hadn't even heard of and they weren't thinking about exponentiation either. How is that possible?

Have we caught your interest? —This is a longer and more detailed article about compound interest and , complete with some history.

Polar power —Like spirals and flowers? Then you'll love polar coordinates and the pretty pictures they allow you to draw. One of those is intimately related to .

Radioactive decay and exponential laws —Arguably, the exponential function crops up more than any other when using mathematics to describe the physical world. This article looks at radioactive decay and exponential laws.

Light attenuation and exponential laws —This is another article that explores the appearance of exponential laws in nature. It explores light attenuation: the way in which light decreases in intensity as it passes through a medium. the a