Picking off more pieces of pi.

The number pi represents the result of dividing a circle's circumference by its diameter. Starting with 3.141592653 ..., its digits go on forever. So far, researchers have computed the first 51.5 billion decimal digits of pi (SN: 8/9/97, p. 92). Using a remarkable formula discovered in 1995, they can also determine specific, individual digits of pi without computing and keeping track of all the preceding digits. The catch is that the formula works for binary, but not decimal digits (SN: 10/28/95, p. 279). Expressed in binary form, pi starts off as 11.0010010000 ....

Now, Colin Percival, a 17-year-old student at Simon Fraser University in Burnaby, British Columbia, has calculated the five-trillionth binary digit, setting a record for the highest known digit of pi. Percival needed 5 months and the help of 25 computers in six countries to complete the calculation. He reported his feat on the World Wide Web at http://www.cecm. sfu.ca/projects/pihex/announce5t.html. However, there is no way to convert that result, 0, into decimal form without knowing all the binary digits that come before the one of interest.

Percival says his next challenge is to finish calculating the 40-trillionth binary digit. The ongoing calculation is distributed among more than 200 computers throughout the world. Beyond that, the quadrillionth binary digit beckons.