No offense meant to pi (especially on Pi Day!), but here's a number I think is way cooler: phi.
You might have heard of it by one of its aliases, like "the golden number" or "the golden ratio" or, simply, 1.618. It's got its own fanclub/website too. Like pi, phi is derived from a special geometry-based ratio. And it also has a relationship with the Fibonacci sequence (1, 1, 2, 3, 5, 8, 13, 21, etc). Take any number in that sequence and divide it by the previous number and you get a value very close to phi -- and it gets closer and closer as the Fibonacci sequence gets longer.
What's really cool and incredible about phi is how it shows up in nature, music, architecture, art and in many other ways throughout the universe.
In architecture, it shows up in the triangular dimensions of the Egyptian pyramids, the rectangular dimensions of Greek buildings like the Parthenon, and in modern architecture as well.
You can see the ratio in nature -- in the spirals of sea shells and in the arrangements of plant branches and flower petals.
It also shows up in music -- from Beethoven and Mozart to Pink. (See video below about the golden ratio and music.)
I'm only scratching the surface here, so to find out more just fire up the Google machine and you'll stumble upon plenty of resources.
Math friends: What your favorite fact about phi?