Comment by vouaobrasil

I read this book as a first-year undergrad. His style inspired me to go after rigour and proof and was a good start to serious mathematics. I always loved Hardy's work and Hardy and Wright's number theory text was also very nice through my PhD in algebra/number theory. I found Hardy's book much nicer than the contemporary calculus texts with irrelevant pictures and modern-day examples. Just straight math! Not for everyone, but it has classical, austere appeal for those who enjoy such things.