Do you have a favourite number - one you love, one you think stands out from all the others? Author Alex Bellos joins us to talk about his quest to find the world's favourite number and discuss whether numbers really can be magical, mystical and memorable, or whether it's all mumbo jumbo. Why are odd numbers so appealing? Which number strikes fear into some people's hearts? And why do lists of questions like these always come in threes? This programme was first broadcast on the BBC World Service.