The first 31 digits of Pi, a greek letter that represents the numerical relationship between a circle's diameter and circumference, amongst other things, if a line from one side of the circle throught its centre and to the opposing side,(its diameter) is equal to one, then its circumference is equal to Pi. In addition the surface area of a circle can be calculated by the formula Pi r2 where r equals the radius of the circle, (half the diameter), Pi times r times r.