Some time ago I was in an airport bookshop waiting for my flight and looking for something to read. I was in the non-fiction section when my eyes alighted on "Alex's Adventures in Numberland". It looked interesting, so I bought it.
It turned out to be a fantastic read and also gave me heaps of ideas for puzzles. This is the second in the series.
Reading the book may give you the answer, it is not necesarry to solve the puzzle.