# An Unbounded Spigot Algorithm for the Digits of Pi

*Jeremy Gibbons*

### Abstract

Rabinowitz and Wagon (*American Mathematical Monthly* 102(3):195–203, 1995) present a *spigot algorithm* for computing the digits of π. A spigot algorithm yields its outputs incrementally, and does not reuse them after producing them. Their algorithm is inherently *bounded*; it requires a commitment in advance to the number of digits to be computed, and in fact might still produce an incorrect last few digits. We propose two *streaming algorithms* based on the same characterization of π, with the same incremental characteristics but without requiring the prior bound.

Journal

American Mathematical Monthly

Month

April

Note

Reprinted on p245−257 of "Pi: The Next Generation"‚ ed David H. Bailey and Jonathan M. Borwein‚ Springer 2016‚ ISBN 978−3−319−32377−0

Number

4

Pages

318−328

Volume

113

Year

2006

*Video of talk at IIJ in March 2017, Part 1*

*Video of talk at IIJ in March 2017, Part 2*