Sue Lawley's castaway this week believes he has the answer to "life, the universe and everything". According to mathematician Ian Stewart, it's 137-and-a-half degrees.

He calls it "the golden angle", and says it can be found everywhere in nature - whether in the pattern of seeds on a sunflower head or in the spiral of a snail's shell. Mathematics, he says, has nothing to do with arithmetic and everything to do with being able to pack the luggage into the boot of the car. But for a broken collarbone which meant he stayed at home working out puzzles with his mum, he would have remained bottom of the class and never discovered how much fun maths could be.

[Taken from the original programme material for this archive edition of Desert Island Discs]

Favourite track: Scarborough Fair by Simon and Garfunkel