Pi by the billions.

The number pi ([Pi]) represents the ratio of a circle's circumference to its diameter. Starting with 3.141592653 ..., its digits go on forever. That hasn't stopped researchers from trying to calculate as many of those digits as computer technology and mathematical methods allow. Last month, computer scientist Yasumasa Kanada and his coworkers at the University of Tokyo Information Technology Center announced computing 206,158,430,000 decimal digits of pi, surpassing their own previous world record of 51,539,600,000 digits (SN: 8/9/97, p. 92). The researchers did the calculation twice, with two different methods. Using two multiprocessor computers, one computation required about 37 hours, and the other, 46 hours.

"It is a pretty spectacular computation," says Jonathan M. Borwein of Simon Fraser University in Burnaby, British Columbia. The accomplishment "highlights just how far both software and hardware have come," he adds. Even a desktop computer can now calculate as many as 1 billion digits of pi.

Kanada took advantage of significant improvements in the efficiency of software for performing the underlying arithmetic and for passing information from one computer processor to another. He also needed an enormous amount of computer memory to achieve the record. "It is very tricky to do these large calculations," notes David H. Bailey of the Lawrence Berkeley (Calif.) National Laboratory.

The 206,158,430,000th decimal digit of pi (not counting the initial digit, 3) is 4. Kanada is now checking the computed digit string to determine how often each digit appears and to identify any interesting patterns among the digits.