Conway J., Guy R. The Book of Numbers 1995

Textbook in PDF format

Journey through the world of numbers with the foremost authorities and writers in the field. John Horton Conway (1937 - 2020) and Richard K. Guy are two of the most accomplished, creative, and engaging number theorists any mathematically minded reader could hope to encounter. In this book, Conway and Guy lead the reader on an imaginative, often astonishing tour of the landscape of numbers.
The Romance of Numbers.
Figures From Figures: Doing Arithmetic.
And Algebra by Geometry.
What Comes Next?
Famous Families of Numbers.
The Primacy of Primes.
Further Fruitfulness of Fractions.
Geometric Problems and Algebraic Numbers.
Imagining Imaginary Numbers.
Some Transcedental Numbers.
Infinite and Infinitesimal Numbers