An irrational number that represents the ratio of the circumference of a circle to its diameter.


  • The number pi is represented by the Greek letter π. It is an irrational number that does not have a repeating decimal representation.
  • The number π is one of the most important constants in mathematics. It is also often used in physics and in engineering.
  • The approximate value of π to the nearest ten-thousandth is 3.1416

Historical note

The Greek letter π has been used to represent the number pi since the 18th century. It is the first letter of the Greek word for “circumference.”

In November 2016, a new world record was established; the value of π was computed to more than 22 trillion decimal places, or more than 22 × 1012 decimal places. This number contains the sequences of all the telephone numbers of the world’s inhabitants. The name of every person on Earth can also be found by replacing the numbers with the letters of the alphabet that have the same rank.

Leonard Euler is believed to have popularized the use of the letter π as a symbol in a book published in 1737. The symbol appeared for the first time in 1706 in the book Synopsis Palmariorium Matheseos, which was written by the English mathematician William Jones

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