Here is the list of reference books and notes that are extremely useful for understanding or reviewing for Mathematics papers of Landau Theoretical Minimum; both I and II. Notes are freely available and are linked to the name.

- Asymptotic Methods in Analysis – N.G.de Bruijn

Most useful in learning how to approximate quantities in calculus-like setting.

- Problems in Mathematical Analysis – Demidovich

Contains tons of mathematical problems with specially challenging (at-least to me) sections on limits, differential equation

- A course in mathematical analysis – Nikolsky

A two volume book containing important concepts like Limits of sequence and limits of functions

- An introduction to asymptotic analysis – Malham [LECTURE NOTES]

A nice and short notes that covers everything one need for Asymptotic analysis.

- Diﬀerential Equations and Linear Algebra – Malham [LECTURE NOTES]

Again nice set of notes with excellent examples of DE and has bunch of problems to be solved.

The complete book for Calculus of Single Variable. Contains illustrated problems along with problems that are left at the reader to solve.

The only complete and most rigorous book on Vector and Tensor Analysis.

- Undergraduate notes of University of Strathclyde [LECTURE NOTES]

Pretty useful as a revision but lacks certain topics.

Some of the books are out of print and may be found in desired electronic format from Library Genesis.