Stillwell's books are very good, as are Courant/Robbins What is Math and Ian Stewart's several books(one with David Tall as collaborator). My dad gifted me Wha

Stillwell's books are very good, as are Courant/Robbins What is Math and Ian Stewart's several books(one with David Tall as collaborator). My dad gifted me What is Math in grade school and i return to it every couple of years.