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The number π (/ p aɪ / ⓘ; spelled out as "pi") is a mathematical constant, approximately equal to 3.14159, that is the ratio of a circle's circumference to its diameter.It appears in many formulae across mathematics and physics, and some of these formulae are commonly used for defining π, to avoid relying on the definition of the length of a curve.
Later computers calculated pi to extraordinary numbers of digits (2.7 trillion as of August 2010), [4] and people began memorizing more and more of the output. The world record for the number of digits memorized has exploded since the mid-1990s, and it stood at 100,000 as of October 2006. [6]
Proofs of the mathematical result that the rational number 22 / 7 is greater than π (pi) date back to antiquity. One of these proofs, more recently developed but requiring only elementary techniques from calculus, has attracted attention in modern mathematics due to its mathematical elegance and its connections to the theory of Diophantine approximations.
In the 1760s, Johann Heinrich Lambert was the first to prove that the number π is irrational, meaning it cannot be expressed as a fraction /, where and are both integers. In the 19th century, Charles Hermite found a proof that requires no prerequisite knowledge beyond basic calculus .
This is a list of topics related to pi (π), the fundamental mathematical constant.. 2 π theorem; Approximations of π; Arithmetic–geometric mean; Bailey–Borwein–Plouffe formula
The number 355 ⁄ 113 is also an excellent approximation to π, attributed to Chinese mathematician Zu Chongzhi, who named it Milü. [5] This approximation is better than any other rational number with denominator less than 16,604.
"The amazing number π " (PDF). Nieuw Archief voor Wiskunde. 5th series. 1 (3): 254– 258. Zbl 1173.01300. Kazuya Kato, Nobushige Kurokawa, Saito Takeshi: Number Theory 1: Fermat's Dream. American Mathematical Society, Providence 1993, ISBN 0-8218-0863-X
Pi 3.14159 26535 89793 ... where agm is the arithmetic–geometric mean and ... The number Λ such that ...