Pi is more than just a number. So it's only appropriate that Pi Day -- today, March 14 -- celebrates more than just 3.14: Pi is like a beguiling lover who can never be truly known. It's a mathematical constant. And yet, it's irrational. Pi transcends reason as it skips off into infinity.

The dry explanation for pi is this: a mathematical calculation symbolizing the relationship between a circle's diameter and its circumference. For mere mortals, that ratio can be represented simply as 3.14.

But a true calculation goes on for much longer than that.

And therein lies the mystery of pi.

For centuries, mathematicians have tried to crack pi's code. Supercomputers have calculated pi to more than a trillion decimal places, searching for a pattern.

"No number has captured the attention and imagination of people throughout the ages," says David Blatner, author of the book "The Joy of Pi." The mere representation of the Greek symbol of pi -- seen above -- sends pi enthusiasts into a tizzy.