Bailey-Borwein-Plouffe formula

The Bailey-Borwein-Plouffe formula, called the BBP formula, is a formula for pi. It was discovered in 1995 by Simon Plouffe and is named after the authors of the article in which it was published, David H. Bailey, Peter Borwein and Plouffe. The formula gives rise to a spigot algorithm that computes the nth hexadecimal digit of pi, and so also the 4nth binary digit, without computing the preceding digits. It does not extract decimal digits directly. Its existence was a surprise, because it had been widely believed that computing the nth digit of pi is as hard as computing the first n digits. Projects such as PiHex have used BBP and BBP-inspired algorithms in distributed computing, and formulas of the same general form have since been found for many other irrational numbers.