I started this topic just to tell the people on Brilliant.org about one of the greatest site I have seen. Since August (2012) I have been using a website called Coursera.org. It is a collaboration of several world renowned universities including names like Stanford, Univ of Toronto, Columbia Univ, California Institute of Technology, etc. These colleges and universities offer courses on different topic like Calculus, Programming, Biotechnology, Algorithms, Business, Health, Mathematical Thinking, Algebra, Earth Sciences, Physics and many more.
These courses are taught by one of the best professors in the field. These courses are absolutely free and you also get a certificate if you qualify all the quizzes, assignments, etc. In my opinion Coursera.org is better than MIT OCW, edX, Udacity, KhanAcademy and other free-education sources.
I would recommend you to take some of the following courses :
i) Calculus : Single Variable - University of Pennsylvania
ii) Analytical Combinatorics, Part I - Princeton University
iii) Analytical Combinatorics, Part II - Princeton University
iv) Linear and Discrete Optimization - Some European College(but course is in english)
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