The Circle Constant

Pi is the ratio of any circle's circumference to its diameter, about 3.14159. Make a circle bigger or smaller and this ratio never changes. It is built into the shape itself.

Pi never ends and never repeats, so no fraction can capture it exactly. Computers have chased its digits past 100 trillion, and the computed digits behave much like random digits in many statistical tests. But mathematicians still have not proved that pi is normal, so its long-run digit pattern remains an open question.