. "The number \u03C0 is a mathematical constant, the ratio of a circle's circumference to its diameter, commonly approximated as 3.14159. It has been represented by the Greek letter \"\u03C0\" since the mid-18th century, though it is also sometimes spelled out as \"pi\" (/pa\u026A/).Being an irrational number, \u03C0 cannot be expressed exactly as a fraction (equivalently, its decimal representation never ends and never settles into a permanent repeating pattern)."@en . .