Not Just Fun and Games; Great Minds; Exclusive Online Issues; by Mark Alpert; 3 Page(s)

Stepping into John H. Conway's office at Princeton University is like stepping into a mathematician's playpen. Dozens of polyhedra made of colored cardboard hang from the ceiling like mirror balls at a discotheque. Dangling among them is a Klein bottle constructed from chicken wire. Several models of crystal lattices sit beside the window, and a pyramid of tennis balls rises from the floor. At the center of it all is Conway himself, leaning back in his chair, his face obscured by oversize glasses and a bushy, gray beard. The eclectic 61-year-old mathematician is clearly in his element.

What's your date of birth? he asks me soon after we shake hands. "April 19, 1961," I reply. "Tuesday!" he shouts immediately. Then he corrects himself. "No, damn! Wednesday!" Slightly irritated by his error, he explains that long ago he devised an algorithm for determining the day of the week that any given date falls on. Called the Doomsday Rule, the algorithm is simple enough for Conway to do the calculations in his head. He can usually give the correct answer in under two seconds. To improve his speed, he practices his calendrical calculations on his computer, which is programmed to quiz him with random dates every time he logs on.