Celebrating Math With Matty Boy

I really enjoy when someone expresses an interest in something that I have a degree of familiarity with, but displays a knowledge deeper and a passion greater than my own about it.

Their excitement about a subject is often infectious, and their posts are a pleasure to read.

In honor of Matty Boy and his ongoing series of posts on math, I present one of my favorite equations:

1111² = 1234321

So, what's your favorite mathematical equation?