Pi, which is represented by the Greek letter π, is a ratio between the diameter of a circle and the circumference of that circle, this ratio is consistent with circles of all sizes. Pi has a value of approximately 3.14. It has been calculated to over two billion digits using computers, but there is no practical use for this number of digits - the circumference of the Earth's orbit around the sun can be calculated within 100m using less then 100 digits.

Pi is an irrational number which means it will go on infinitely without repeating or ending in zeros. Pi is also a transcendental number; this is a number which can not be expressed using a finite number of mathematical operations. Ferdinand Lindmann, a German mathematician proved Pi to be a transcendental number in 1882.

Pi is believed to have been first discovered by the Babylonians around 2000 B.C. The Egyptians are beleived to have found the value around the year 1650 B.C. The earliest known reference to Pi is found in a Middle Kingdom papyrus scroll written by a scribe named Ahmes. At the end of the scroll, he has various mathematical problems and their solutions, including a rough version of Pi.

Around 200 B.C., Archimedes found that Pi was around 3.14. One method he used to calculate the value of Pi was to fill a circle with many sides polygons, which could have their area calculated. This left only one unknown, Pi, which could easily be found. Archimedes used a 96 sided polygon and found the value of Pi to be between 3.140 and 3.142.

Ptolemy calculated Pi to 4 decimal places near the year 200 A.D., using the same method.

The Chinese used the same method of finding the value of Pi as Archimedes. Around 300 A.D., Chung Huing fit a 192 sided polygon into a circle, and later on fit one of 3072 sides. This allowed him to calculate Pi to five digits, 3.14159, which was one more decimal place then the Greeks. The next significant landmark in the history of Pi is in fifth century when two Chinese men, Tsu Ch'ung-Chih and Tsu Keng-Chih (father and son), used a circle with a diameter of ten feet to calculate Pi, the number of sides on the polygon has been lost. The value they found for Pi is 3.1415929203. About nine hundred years later, Chao Yu-Ch'in, another Chinese mathematician, used a 16 384 sided polygon to confirm the calculation made by the Tsu family.

In the 17th century, Pi was called the Ludolphian number, after Ludolph van Ceulen, a German mathematician. The Greek symbol was first adopted by William Jones, an English mathematician, in 1706, but the use of the symbol did not become popular until 1737 when the Swiss mathematician Leonhard Euler adopted it.

The value of Pi continues to be calculated everyday using super computers all around the world, trying to find the most precise value of Pi, a process which could go on forever because the exact value can not be found.

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