The Royal Mail says UK stamp prices are still among the best value in Europe, despite an imminent steep price rise. Tim Harford finds out whether this is true, and compares the price of postal services around the world. Plus, he finds out how, after being invented by Indian mathematicians, modern numbers became established in the ancient Arab world and then journeyed on to Europe in what was essentially the first maths textbook ever written, "Liber Abaci". Its author was Leonardo of Pisa, better known as Fibonacci. Tim speaks to Keith Devlin, author of The Man of Numbers, to find out more. This programme was first broadcast on the BBC World Service.