I believe many of his books (at least, those which I picked up, I know he wrote many more) were collections of his Scientific American "Mathematical Games" colu

I believe many of his books (at least, those which I picked up, I know he wrote many more) were collections of his Scientific American "Mathematical Games" columns. And as a bit of trivia - when Douglas Hofstadter (of Gödel Escher Bach) took over the slot in the early 1980s, he renamed it to the anagrammatic "Metamagical Themas".