Why we all love numbers

We cannot help but react to numbers, but why are odds masculine and evens feminine? Why were Levi's 501s and WD-40 given those names? And is number 3 really 'warm' and 'friendly'? Alex Bellos does the maths

What book would you send to a prisoner?

Regulations introduced by the justice secretary Chris Grayling that stop people sending books to prisoners in England and Wales, have caused outrage among writers, teachers and prison experts. But what titles would they send?