
Since its original publication in 1990, Kenneth Falconer's Fractal Geometry: Mathematical Foundations and Applications has become a seminal text on the mathematics of fractals. It introduces the general mathematical theory and applications of fractals in a way that is accessible to students from a wide range of disciplines. This new edition has been extensively revised and updated. It features much new material, many additional exercises, notes and references, and an extended bibliography that reflects the development of the subject since the first edition. Provides a comprehensive and accessible introduction to the mathematical theory and applications of fractals. Each topic is carefully explained and illustrated by examples and figures. Includes all necessary mathematical background material. Includes notes and references to enable the reader to pursue individual topics. Features a wide selection of exercises, enabling the reader to develop their understanding of the theory. Supported by a Web site featuring solutions to exercises, and additional material for students and lecturers. Fractal Geometry: Mathematical Foundations and Applications is aimed at undergraduate and graduate students studying courses in fractal geometry. The book also provides an excellent source of reference for researchers who encounter fractals in mathematics, physics, engineering, and the applied sciences.
I remember getting God Created The Integers when I was a teenager and... not finishing it. I also got a copy of Brown & Churchill's Complex Variables and Applications and spent hundreds of hours on it. As a teenager, I preferred textbooks with problem sets to popularizations. (I still do.) Of course, this was [complex] analysis, so it doesn't qualify.
One book which is fully technical but also entertaining by way of the subject matter, and which was inspiring to me around 14-15, was Kenneth Falconer's Fractal Geometry:
https://www.amazon.com/Fractal-Geometry-Mathematical-Foundat...
Of course, at that age, I didn't understand what Falconer meant by describing the Cantor set as "uncountable", or what a "topological dimension" was, but I was able to grasp the gist of many of the arguments in the book because it is very well illustrated and does not rely too much on abstruse algebra techniques. Some people don't enjoy reading a book if they don't fully understand it, but I liked that kind of thing. As I got older and learned more, I started to be able to understand the technical arguments in the book as well.