I would like to have some suggestions about serious (that is, with good mathematical content) but fun books that cover topics (or propose problems)
- in "recreational mathematics";
- in any other field (but from a perspective that is not presented in standard university courses).
For example, I would appreciate some references to books by Martin Gardner and John Conway.
- On Numbers and Games, by John Conway (which was not an answer actually);
- Generatingfunctionology, by Herbert Wilf;
- The Symmetries of Things, by John Conway;
- The Sensual (Quadratic) Form, by John Conway.
But I would like to know other opinions on the books proposed in these threads and on other books (also newly published ones).