Alex Bellos is surprised that people ask him what his favorite number is, so he decides to ask everyone what theirs is.

Alex Bellos is the author of the popular science bestsellers The Grapes of Math and Here's Looking at Euclid. In a previous life he was the Guardian's South America correspondent, based in Rio, where he wrote Futebol: the Brazilian Way of Life, a book on Brazilian football. He also ghost-wrote Pele's autobiography. Alex blogs on maths for the Guardian and presents maths documentaries for BBC Radio 4. His YouTube clip on how to cut a cake has had more than 6.5 million views.

This story originally aired on January 26, 2015.