The number (/pa/) is a mathematical constant that is the ratio of a circle's circumference to its diameter. The constant, sometimes written pi, is approximately equal to 3.14159. It has been represented by the Greek letter "" since the mid-18th century. is an irrational number, which means that it cannot be expressed exactly as a ratio of two integers (such as 22/7 or other fractions that are commonly used to approximate ); consequently, its decimal representation never ends and never repeats. It is a transcendental number a number that cannot be produced with a finite sequence of algebraic operations (sums, products, powers, and roots). The transcendence of implies that it is impossible to solve the ancient challenge of squaring the circle with a compass and ruler. The digits in the decimal representation of appear to be random, although no proof of this supposed randomness has yet been discovered.
Because is closely related to the circle, it is found in many formulae f