Think of a Number

How many colors are needed to color a map? Must hailstones numbers always fall to the ground? Can statistics prove anything? What is a perfect square, and who has found the ultimate one? How do numbers affect national security? What kinds of problems confront the traveling salesman? Does anyone know how best to pack balls together? What is life like in 4 (or 3 1/2) dimensions? How does a clock cou...