March 14, written out as 3/14 in the US and a few other countries, is π day, as those are the first three digits of the famous number.

π is one of the most important and fascinating numbers in maths.

Happy π day!

March 14, when written out in the American date style of month/day, comes out as 3/14. That coincides with the three first digits of π: 3.14.

π is one of the most important numbers in maths. As you may recall from basic geometry, π is defined as the ratio of a circle’s circumference to its diameter. So, anywhere where circles or cyclical things show up, π tends to show up as well. It would be impossible to do geometry, trigonometry, calculus, analysis of waves, or most branches of maths without the concept of π.

As a number, π is also itself fascinating. π is an irrational number – it can’t be written as a fraction of two integers, no matter what integers you choose. One consequence of that is that the infinite decimal expansion of π never adopts a repeating pattern.

π is actually a step further than an irrational number, and is what mathematicians call a transcendental number. There are plenty of irrational numbers – the square root of 2, or 3, or any prime number is irrational, as are cube roots and higher-power roots of primes. Transcendental numbers, like π, aren’t the roots of any rational number. Another way of saying that is that π raised to any power is still irrational.

π day comes with a few caveats, the biggest being that most of the world doesn’t write March 14 as 3/14, but instead as 14/3. Still, for residents of the countries that do, π day offers a fun chance to reflect on a very special number.

Want to read a more in-depth view on the trends influencing Australian business and the global economy? BI / Research is designed to help executives and industry leaders understand the major challenges and opportunities for industry, technology, strategy and the economy in the future. Sign up for free at research.businessinsider.com.au.