The number 3,141592 …, which in Spanish is read “pi”, is the **symbol of the quotient between the circumference and its diameter** and represents, therefore, one of the most perfect geometric shapes. The symbol was used for the first time to represent this reason in the year **1706 by the mathematician William Jones** , but it was the Swiss **Leonhard Euler** who popularized its use from 1737. It is an irrational number, with an infinite number of figures. decimals, of which several million have already been calculated using supercomputers.

The **number pi** is present in spheres, cones, cylinders, ellipses … And also in nature. Thus, for example, Hans-Henrik Stolum, a geologist at the University of Cambridge, calculated the relationship between the actual length of rivers, from the source to the mouth, and their length measured in a straight line, and found that the relationship is approximately 3.14. And if we multiply the diameter of the elephant’s foot by twice pi, the result obtained is the height of the animal. Another curious fact: the height of the pyramid of Cheops divided by its base results in this irrational number.

The **world day of the number Pi** is celebrated on March 14, since in the Anglo-Saxon world the date is written 3/14. The day of the approach to Pi is celebrated on July 22 due to the similarity of the quotient 22/7 with the number Pi.

## A little further back in history

Pi (π) has been known for almost 4000 years, but even if we calculate the number of seconds in those 4000 years and calculate pi at that number of places, we would only be approximating its true value.

The ancient Babylonians calculated the area of a circle by taking 3 times the square of its radius, giving a value of pi = 3. A Babylonian tablet (ca. 1900–1680 BC) indicates a value of 3.125 for pi, which is a closer approximation.

The Rhind Papyrus (ca.1650 BC) gives us an idea of the mathematics of ancient Egypt. The Egyptians calculated the area of a circle using a formula that gave the approximate value of 3.1605 for pi.

The first calculation of pi was made by **Archimedes of Syracuse** (287–212 BC), **one of the best mathematicians of the ancient world.** Archimedes approximated the calculation of the area of a circle using the Pythagorean Theorem to find the areas of two regular polygons: the polygon inscribed within the circle and the polygon within which the circle was circumscribed. Since the actual area of the circle lies between the areas of the inscribed and circumscribed polygons, the areas of the polygons gave upper and lower limits for the area of the circle. **Archimedes knew that he had not found the value of pi but only an approximation within those limits** .

**Zu Chongzhi** (429–501), a brilliant Chinese mathematician and astronomer, used a similar approach. Zu Chongzhi would not have been familiar with Archimedes’ method, but because his book was lost, little is known about his work. Che calculated 3.14 as an approximate value of Pi and showed it in the form of the fractions 157/50 and 3927/1250.

Mathematicians began using the Greek letter pi in the 1700s.

## Digits of pi

The first 100 digits of pi are:

3.14159 26535 89793 23846 26433 83279 50288 41971 69399 37510 58209 74944 59230 78164 06286 20899 86280 34825 34211 7067

The website *piday.org* has pi included within the first million digits, in case you’re curious.