## Articles

*Plus*takes an illustrated tour of an extraordinary geometric construction: the

**Klein bottle**.

**number 23**.

**Riemann Hypothesis**is probably the hardest unsolved problem in all of mathematics, and one of the most important. It has to do with prime numbers - the building blocks of arithmetic. Nick Mee, together with Sir Arthur C. Clarke, tells us about the patterns hiding inside numbers.

**data compression**.

**Isaac Newton**and David Gregory - took place on the campus of Cambridge University. The discussion concerned the

**kissing problem**, but it was to be another 260 years before the problem was finally solved.

**Medical statistics**can help us to decide what treatment to look for when we are ill, and to estimate our chances of recovery.

**Golden Ratio**, and ever since people have been fascinated by its extraordinary properties. Find out if beauty is in the eye of the beholder, and how the Golden Ratio crosses from mathematics to the arts.

*Plus*meets mathematician, author and broadcaster

**Simon Singh**to find out about the science of secrecy.