03/14/2015 is Pi day because of it's more common expression, 3.1415
Pi is unique because it never reaches a conclusion of exactness no matter how far you calculate it.
I'm not going to pretend to have a handle on this. However The New York Times had a good write up piece on this today.
Maybe this music video will help
I'm certain a lot of people may doubt my numbers. I'd really appreciate someone doing the math to verify my accuracy. Here's an excellent site that provides several formulas for calculating Pi
Please get back to me when you're done.
Thanks & you're welcome :-)