Today, Saturday 3/14/15 is PI Day. The first 5 digits of pi is 3.1415. "The number π is a mathematical constant that is the ratio of a circle's circumference to its diameter, and is approximately equal to 3.14159. It has been represented by the Greek letter "π" since the mid-18th century." - from Wikipedia. Pi Day occurs once a century. The next Pi Day is 3/14/2115.