Apparently, I missed *e Day*. More than likely, so did you. Don’t worry, though, there will be another chance this year, though you’ll be celebrating with Europeans.

Rhett Allain didn’t miss *e Day*:

Why is Feb. 7 e Day? Well, in the USA we use the Middle-endian date format. So, Feb. 7 would be commonly written as 2/7/13. Guess what? The first two digits of e are 2.7. If you live in other places you might use the little-endian date format. In this case 2/7/13 would be July 2. For those people, just consider this an early post.

But don’t get distracted. (Yes, my first question was the same as yours: “*Really? It’s *really* called ‘Middle-endian’?*”

But *e Day* is a celebration of *e*, the jealous little brother of π.

Allain offers his favorite definition: “*e is the number that if you raise that number to the power x, the slope of the function is the same value as the function.*”

And it just goes downhill from there. Or uphill, I guess, if you look at it on a graph. Sort of. The graph at right does not show you *e*. Maybe you could try reading the Wikipedia entry on *e*, but that’s the fun thing about being a poor mathematician and clueless excuse for a scientist.

Sometimes called Euler’s number after the Swiss mathematician Leonhard Euler, e is not to be confused with γ—the Euler–Mascheroni constant, sometimes called simply Euler’s constant. The number e is also known as Napier’s constant, but Euler’s choice of this symbol is said to have been retained in his honor.

By the time you get to the part about *derangements*, well, yeah.

Oh, right. *e* = 2.71828 (and a whole bunch of numbers after that; it’s irrational *and* trancendental, just like π).