To understand recursion get "The Little Lisper" or the later book "The Little Schemer". To know when not to use recursion and use iteration instead, look at "Al

To understand recursion get "The Little Lisper" or the later book "The Little Schemer". To know when not to use recursion and use iteration instead, look at "Algorithms + Data Structures = Programs" and finally, you can delve into the mathematics of primitive and non-primitive recursive function with "Recursive Functions in Computer Theory". Good reading to all.