
The number π (/paɪ/; spelled out as "pi") is a mathematical constant that is the ratio of a circle's circumference to its diameter, 
approximately equal to 3.14159. The number π appears in many formulae across mathematics and physics. It is an irrational number, meaning 
that it cannot be expressed exactly as a ratio of two integers, although fractions such as 22/7 are commonly used to approximate it. 
Consequently, its decimal representation never ends, nor enters a permanently repeating pattern. It is a transcendental number, meaning 
that it cannot be a solution of an equation involving only finite sums, products, powers, and integers. The transcendence of π implies 
that it is impossible to solve the ancient challenge of squaring the circle with a compass and straightedge. The decimal digits of π 
appear to be randomly distributed,[a] but no proof of this conjecture has been found.

For thousands of years, mathematicians have attempted to extend their understanding of π, sometimes by computing its value to a high 
degree of accuracy. Ancient civilizations, including the Egyptians and Babylonians, required fairly accurate approximations of π for 
practical computations. Around 250 BC, the Greek mathematician Archimedes created an algorithm to approximate π with arbitrary accuracy. 
In the 5th century AD, Chinese mathematicians approximated π to seven digits, while Indian mathematicians made a five-digit approximation, 
both using geometrical techniques. The first computational formula for π, based on infinite series, was discovered a millennium later. 
The earliest known use of the Greek letter π to represent the ratio of a circle's circumference to its diameter was by the Welsh 
mathematician William Jones in 1706.