Let us mention here some websites, books, and / or articles related to mathematics which I think you’ll enjoy reading or visiting (since, I myself enjoy reading the books and articles and visiting the websites even today).  

Things to read on mathematics ( Just recommendations and no advertising …)

Here are a few things (websites, books and articles) I would recommend every mathematics enthusiast to read (though I am not advertising anything here) as I myself found them interesting.

  1. Art of Problem Solving (AOPS) One of the best mathematics forums for discussion on high school mathematics including high school mathematics olympiads and also college level mathematics (I myself learned a big part of whatever mathematics I know today from this website by visiting the forums).
  2. Art of Problem Solving articles Some articles of interest to students of problem solving.
  3. Number Theory Guy A collection of teaching resources maintained by my friend Justin Stevens. Here you can also access his number theory book (which also happens to be one of my favourite number theory books).
  4. Power Overwhelming (USAMO) This mathematics blog is maintained by my friend Evan Chen. Here you can also find his mathematics notes collection (“an infinitely large napkin”) which is mainly focused on college level mathematics.
  5. Romanian Mathematical Magazine (RMM) It is a mathematical magazine which features selected articles, mathematics notes, problems and solutions sent by people from all across the globe. It is maintained by Daniel Sitaru and other editors of the RMM. The online version of it is free to access. 
  6. Fedya Petrov’s blog — A website on mathematical contents created and managed by my teacher Professor Fedor Petrov.
  7. The Fibonacci Quaterly A journal on various things related to the Fibonacci sequence and the Fibonacci numbers. 
  8. Mathematical drawings by MC Escher The official website of MC Escher which features several mathematical drawings. A wonderful website to visit if you are interested in mathematics and / or drawings. 
  9. Tanya Khovanova’s blog — A mathematics blog maintained by Tanya Khovanova.
  10. The Greek Mathematics (mathematica) forum A wonderful mathematics discussion forum (some problems are written in the Greek language but you can translate or probably take the help of some Greek friend if you have any). 
  11. Mathkalender website A website on mathematics at different levels of different syllabus. And they host a contest every Christmas featuring beautiful mathematics (and a nice story motivating the mathematical problem). 
  12. Chess Problems by Richard Stanley A collection of resources on chess puzzles maintained by Richard P. Stanley.  
  13. A list of mathematics websites maintained by AOPS — Woah ! I just saw it. Seems pretty good. I am happy that such a list exists. Authentic and validated. Visit the link for more details. 
  14. Yufei Zhao Notes Mathematical Olympiad training handouts by Yufei Zhao.
  15. Notes delivered by Ben Green — Here you can find some lecture notes prepared and delivered by prof. Ben Green at Oxford. 
  16. Mathematical Excalibur — A magazine which mainly discusses on problem solving in mathematics usually at the Olympiad level.
  17. Crux Mathematicorum — The CRUX Mathematicorum is a mathematics magazine published by the Canadian Mathematical Society. 
  18. Statistical Inference Book — A book on Statistical Inference authored by George Casella and Roger L. Berger.
  19. Grotex’s Hut — A mathematics blog maintained by my friend He Jiahao from People’s Republic of China. 
  20. List of some publications by prof. Fedor Petrov
  21. Website of Amir Hossein Pavardi — The official website of Amir Hossein Pavardi. 
  22. Easy Beautiful Math — A beautiful mathematics group created and maintained by my friend and guide Lorian Saceanu. 
  23. Seoneo’s blog — A mathematics blog maintained by friend Seoneo from Korea.  
  24. Some Person Over Here website — A mathematics website (mainly focused on college level mathematics) maintained by friend James Leng. 
  25. EXPII — The expii mathematics website is started and maintained by Po Shen Loh and his team (some of my friends are actually a part of the team and some others write there). 
  26. Secrets in Inequalities Volume 1 book A wonderful book on mathematical inequalities (from the Mathematical Olympiad level).  
  27. MATHEMATICAL INEQUALITIES VOLUME 2 Vasile Cirtoaje — A more advanced book on mathematical inequalities featuring some strong inequality solving techniques. 
  28. Topics In Number Theory Visit here for the number theory book by Amir Hossein Parvardi (which is really a very good book) and here you can also enrol for his online classes on number theory. 
  29. Introduction To Numerical Analysis F.B Hildebrand A book on Numerical Analysis which I found quite interesting and easy to read. It starts with discussion on even the preliminary notions.
  30. An Introduction To Set Theory William A.R. Weiss A book on set theory featuring the axiomatic treatments of sets.
  31. Set Theory Notes Tony Lian A quick set of notes on set theory axioms. 
  32. Website of C J Quines Website maintained by friend Carl Joshua Quines.
  33. Harvey Mudd College Fun Mathematics — A website on fun facts in mathematics maintained by Harvey Mudd College. 
  34. Cezar Lupu website — Mathematics website maintained by Cezar Lupu. 
  35. Mathematics website of BQ sir A mathematics website created and maintained by Bao Qian sir. It is written in Chinese language but it is an excellent website.
  36. Collection of mathematical inequalities and solutions by Luofangxiang sir — A collection of solutions to mathematical inequality problems by my friend (and a guide too) Luo Fang Xiang. Here you’ll see some of the most elegant techniques to solve mathematical inequality problems. As rightly said his methods work like magic.
  37. Schaum’s Outline Of Linear Algebra — A good book on Linear Algebra. It has some interactive problems which adds to the fun of studying the subject. 
  38. Linear Algebra Jim Hefferon Book — A book on Linear Algebra written by Jim Hefferon.
  39. Sketches of Topology A mathematics website on topology.
  40. IB Mathematics Resources Developed and maintained by British International School, Phuket, Thailand. 
  41. 3Blue1Brown — A website dedicated to mathematics demonstrated through animation. Some concepts gets super simplified when you see the demonstrations. 
  42. Tolaso Mathematics — A mathematics website maintained by my friend Tolaso K. Jos.  Here you can also find a forum where some really good quality problems are discussed.
  43. Mathimatikoi Forum A mathematical discussion and problem solving forum.
  44. Elementary Geometry for College Students — A book on elementary geometry. It starts from a very basic level and moves to more advanced discussions.
  45. HBCSE Olympiad website The official website for all Olympiads organised in India.
  46. Another mathematics links collection Yet another collection on mathematical links (some of the links I previously mentioned were taken from here with no intention of double mentioning). It is maintained by a user at University of Crete, Greece.
  47. Functional Equation book A very well written book on Functional Equations with lots of problem solving in it. It is written by Amir Hossein Parvardi. 
  48. How to Lie with Statistics — An interesting book on statistics.
  49. Mathematical Circus — A recreational mathematics book authored by Martin Gardner.
  50. R for dummies — An interesting and easy to read type book for learning the basics of the programming language R starting right from the beginner level.
  51. Professionally formatted mathematical nonsense  This maybe helpful if someone needs lots of papers one day!
  52. Mathematical Homepages — A collection of links (mainly to homepages of some mathematicians) which was shared by Prof. W. T. Gowers on his homepage at Cambridge. 
  53. Gowers’ weblog — Weblog maintained by Prof. W. T. Gowers. Among the most informative weblog I have ever visited. If you are already acquainted with the works of Prof. W. Timothy Gowers, you will know that he is a brilliant mathematics demonstrator (and of course among the legendary mathematicians of the century). 
  54. What’s New — Weblog maintained by Prof. T. Tao. Alongside the weblog of Prof. W. T. Gowers this stands out as an exceptionally well written mathematics website. Perhaps my interest of maintaining a mathematics weblog developed from the inspiration I gained by reading some posts on this weblog. 
  55. Mathematical Omnibus: Thirty Lectures on Classic Mathematics — A book by Dmitry Fuchs and Serge Tabachnikov. 
  56. The Old Problem Seminar — The Old Problem Seminar website.
  57. A point of view — The website of my friend D. Grozev illustrates a lot of interesting things in mathematics. 

There are definitely many other mathematical (+fun) resources. So we will be updating this page regularly adding new links and better descriptions. 

Soon I will be uploading handouts prepared by me and / or my friends. 

Also check out the Publications and Problem of the week discussion and Archive  pages of the website.

Hope you enjoy reading them 🙂 .