The book Group Theory Basic Algebra written by Jacobson is good and internationally recognized as an algebra textbook. If undergraduates can read it, it is said that they can do their own research after reading it.

Lecture notes on number theory

Zahlentheorie)

By Dirichlet and Dai Dejin.

Introduction:

The lecture notes on number theory were written by German mathematicians Dirichlet and Dai Dejin, and published in 1863. The handout can be regarded as a watershed between the classical number theory of Fermat, Jacobi and Gauss and the modern number theory of Dai Dejin and riemann sum Hilbert. Dirichlet did not clearly define the central concept group of modern algebra, but many of his proofs showed that he had an implicit understanding of group theory.

analysis situs

James munkres

Introduction:

This wonderful introductory textbook is the standard textbook of university point set topology and algebraic topology. Munkres can use the rigor of mathematics to teach many topics and give the source of concepts intuitively.