The Eternity puzzle is back with a $2 million prize

Last October, two mathematicians won £1m when it was revealed that they were the first to solve the Eternity jigsaw puzzle. It had taken them six months and a generous helping of mathematical analysis. Mark Wainwright meets the pair and finds out how they did it.

You may think that searching for new prime numbers is a job for super-computers. However, on 13th November 1996, Frenchman Joel Armengaud discovered a new one using his humble PC.