What was the first bit of mathematics that made you realize that math is beautiful? (For children's book) I'm a children's book writer and illustrator, and I want to to create a book for young readers that exposes the beauty of mathematics. I recently read Paul Lockhart's essay "The Mathematician's Lament," and found that I, too, lament the uninspiring quality of my elementary math education.
I want to make a book that discredits the notion that math is merely a series of calculations, and inspires a sense of awe and genuine curiosity in young readers.
However, I myself am mathematically unsophisticated.

What was the first bit of mathematics that made you realize that math is beautiful?

For the purposes of this children's book, accessible answers would be appreciated.

When I was a kid I realized that 
$$0^2 + 1\ (\text{the first odd number}) = 1^2$$
$$1^2 + 3\ (\text{the second odd number}) = 2^2$$
$$2^2 + 5\ (\text{the third odd number}) = 3^2$$
and so on...
I checked it for A LOT of numbers :D
Years passed before someone taught me the basics of multiplication of polynomial and hence that $$(x + 1)^2 = x^2 + 2x + 1.$$
I know that this may sound stupid, but I was very young, and I had a great time filling pages with numbers to check my conjecture!!!
