The books by Christian & Griffiths, Hofstadter and Smullyan are on recreational maths. Hofstadter’s is a winner of the Pulitzer Prize. The other titles are textbooks; Hammack’s book is an Open Textbook, just like this book is.
-  Christian, B. and Griffiths, T. (2016). Algorithms to Live By: The Computer Science of Human Decisions. New York, NY: Henry Holt and Co.
-  Critchlow, C. and Eck, D. (2011). Foundations of Computation, version 2.3.1. Geneva, NY: Hobart and William Smith Colleges. math.hws.edu/ FoundationsOfComputation/
-  Epp, S. S. (2011). Discrete Mathematics with Applications, 4th edition. Boston, MA: Cengage Learning.
-  Grassmann, W. K. and Tremblay, J.-P. (1996). Logic and Discrete Mathematics. Upper Saddle River, NJ: Prentice-Hall.
-  Hammack, R. (2018). Book of Proof, 3rd edition. Richmond, VA: Virginia Common- wealth University. www.people.vcu.edu/~rhammack/BookofProof3/
-  Hofstadter, D. (1979). Gödel, Escher, Bach: An Eternal Golden Braid. New York, NY: Basic Books.
-  Huth, M. and Ryan, M. (2004). Logic in Computer Science, 2nd edition. Cambridge, UK: Cambridge University Press.
-  Smullyan, R. M. (1979). What is the Name of This Book? Upper Saddle River, NJ: Prentice-Hall.