There's an old urban legend about a state legislature that passed a law redefining pi so that it equaled 3. This story is a myth - but the true story that inspired it is actually even more ridiculous and bizarre.
DNA isn't just the building block of all complex life...if you give it about eight hours, DNA can also calculate the square root of 15. It's all explained in this video, which awesomely mixes hardcore science with fairy tale storytelling.
There are numbers out there that are so enormously, impossibly vast that to even write them down would require the entire universe. But here's the really crazy thing...some of these incomprehensibly huge numbers are crucial for understanding the world.