Defining the number Pi (π) is easy: it represents the ratio between the circumference of a circle and its diameter. Or, to put it another way, a circle of diameter 1 will have a circumference of length π. But how much is that, π? For school children, the answer is often 3.14. The most picky sometimes push up to 3.1416, a rounding far from the reality of this number, which until this week included 50,000 billion digits behind the comma. After 108 days of computing, a high-performance computer at the University of Applied Sciences in Graubünden, Switzerland, smashed this record by adding 12.8 trillion digits.

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By way of comparison, if we had to print the entire number π at this stage, that would represent some 62 million pounds, estimates Jean-Paul Delahaye, mathematician and computer scientist at the University of Lille (1). The national library of France has just under 16 million books and collections. ” *Not only does no one ever print this number, but no one looks at it*, continues the specialist. *All these decimal places only exist for the computer that calculated them.* “

### Unnecessary precision, but proof of computer advances

For enthusiasts, the last ten digits of π are now 7817924264. A great mathematical feat, but for what use? As summarized by Julia Collins, a mathematician at the Australian University Edith Cowan, in an article on *The Conversation* : “* Ten decimal places are enough to calculate the circumference of the Earth to within a millimeter. With 32 decimal places, we can calculate the circumference of the Milky Way with a precision of the order of the width of a hydrogen atom.*. “

Knowing so many digits behind the comma therefore does not upset our daily life. It is just useful for mathematicians to know if π is a “normal” number, that is to say that each digit and series of digits return at a given frequency, according to given probabilities.

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In reality, as often in science, the result is less important than the means to achieve it. ” *To break such records, it is necessary to develop algorithms capable of handling very long sequences of digits and technologies capable of calculating very quickly, without interruption and without error.*, explains Jean-Paul Delahaye. *It is very useful in cryptography for example.* »Computing, software and hardware power, which is also used in weather forecasts, biology or artificial intelligence.

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