Mathematics: A Discrete Introduction by Edward R. Scheinerman: https://books.google.com/books/about/Mathematics_A_Discrete_Introduction.html?id=DZBHGD2sEYwC ht

Mathematics: A Discrete Introduction by Edward R. Scheinerman: https://books.google.com/books/about/Mathematics_A_Discrete_Introduction.html?id=DZBHGD2sEYwC https://books.google.com/books/about/Mathematics_A_Discrete_... I bought this book when I was ~16 because I wanted to learn some discrete maths, but it actually touches many different interesting topics that you don't see in secondary school (including some cryptography!).