The difference of the squares of any two odd numbers is divisible by 8.This delightful book, if symbolic logic is your idea of fun, combines the story of Lewis Carroll (Alice in Wonderland) and Charles Dodgson (Mathematician at Oxford). With lots of problems and puzzles (from Algebra to Zeno's paradox), the book is a mixture of biography and recreational math - for those that do not see recreational math as an oxymoron.
While many of the puzzles have been reprinted over and over since published by Lewis Carroll over 100 years ago, some were new to me. I enjoyed discovering the flaw in an almost convincing proof that all triangles were isosceles, and seeing, from an age before calculators, problems like:
What is the cube root of 673373097125?Hint for the 21st century: Google cube root of 673373097125.