PHILOMATH: The Geometric Unification of Science & Art Through Number
The Prime Number Conspiracy: The Biggest Ideas in Math from Quanta
A Most Elegant Equation: Euler's Formula and the Beauty of Mathematics
Number Theory: A Very Short Introduction (Very Short Introductions Book 636)
Proof and the Art of Mathematics
How Numbers Work: Discover the strange and beautiful world of mathematics (New Scientist Instant Expert)
Proofs from THE BOOK
Pythagoras: His Life and Teaching, a Compendium of Classical Sources