recreational math 42 was the last remaining number below 100 which could not be expressed as the sum of three cubes – until now Mark Frauenfelder
recreational math Professor Stewart's Incredible Numbers is a delightful book of recreational math Mark Frauenfelder
sinkholes Uh-oh. Huge sinkhole swallows up Illinois soccer field — which was built over a working mine (video) Carla Sinclair
useful stuff Excellent cheap puzzle book: The Moscow Puzzles: 359 Mathematical Recreations Mark Frauenfelder