Pi to ten trillion digits

Some people simply enjoy doing sums for the sake of it. Like the pair of geeks who have just calculated the value of pi to ten trillion digits, according to a report in New Scientist.

Pi, the ratio of a circle’s circumference to its diameter, is an irrational number, meaning that its decimal representation never ends or repeats. It starts with 3.14 and just 36 more digits are sufficient to calculate the circumference of a circle the size of the observable universe with an error no larger than the radius of a hydrogen atom.

So although most of the subsequent ten trillion digits are largely irrelevant, a computer scientist from the US and a systems engineer in Japan spent nearly a year listing them anyway. After fighting computer hard drive failures and narrowly missing disruption due to the Japan earthquake, they beat their own previous Guinness world record of five trillion digits.

Calculating pi has fascinated man for centuries. It was estimated at three in the Bible, while, as Didapper has recorded (PJ, 3 July 2010, p29), the Egyptians came up with 3.16 and the Babylonians reckoned 3.125, both in about 1900BC.

Archimedes got closer with 3.14185, but the Chinese mathematician Zu Chongzhi settled on 3.1415926 in around AD480. This was the most accurate approximation for the next 900 years.

Before computers, the most precise estimation of pi was made to 1,120 digits using a gear-driven calculator in 1948.

But if calculating this extremely long series of numbers is a waste of time, then remembering it must be completely pointless. The Guinness world record for this feat goes to a 24-year-old graduate student from China, who memorised pi to 67,890 digits, a number that took him over 24 hours to recite.