**New Delhi, March 14: **Google on Wednesday celebrated the 30th anniversary of the mathematical constant Pi -- a fundamental element of several mathematical fields -- with a doodle of actual pies.

Google asked Cronut inventor Dominique Ansell to create the doodle for Pi Day which was first recognised by physicist Larry Shaw.

The award-winning pastry chef created the doodle using actual caramel apple pies.

The Google letters in the doodle are constructed from pastry, butter, apple and orange peel.

March 14 is celebrated as Pi Day when the date lines up in the numbers of the famous constant. The day looks like 3/14 for those that write dates in the month/day format, like in the US.

Pi (Greek letter "I") is the symbol used in mathematics to represent a constant -- the ratio of the circumference of a circle to its diameter -- which is approximately 3.14159.

In geometry, 'Pi' plays an important constant in finding out the area of a circle.

According to piday.org, Pi has been calculated to over one trillion digits beyond its decimal point.

"As an irrational and transcendental number, it will continue infinitely without repetition or pattern. Pi's infinite nature makes it a fun challenge to memorise, and to computationally calculate more and more digits," it said.

Mathematician Archimedes used polygons with many sides to approximate circles and determined that Pi was approximately 22/7.

The symbol was first used in 1706 by William Jones.

The use of Pi became popular after it was adopted by the Swiss mathematician Leonhard Euler in 1737.