Resources

Community and News

Math.Stackexchange An online community for asking and answering mathematical questions
MathOverflow An online community for research mathematicians that has quite a few prominent members
Mathematics Genealogy Project A tree of supervisors and students in the history of mathematics
Quanta Magazine Well-written articles on recent mathematical and scientific news with beautiful graphics

Encylopaedic Sites

Wolfram MathWorld A mathematical encyclopedia “Created, developed, and nurtured by Eric Weisstein at Wolfram Research”
Encyclopedia of Mathematics A mathematical encyclopedia hosted by the European Mathematical Society
OEIS The On-Line Encyclopedia of Integer Sequences: type in a few terms of a sequence and view matches!
Cut-the-knot A vast array of mathematical posts by Alexander Bogomolny

Typesetting and Graphics

Overleaf LaTeX typesetting in an online setting without any downloading needed and with lots of packages installed
LaTeX Tables Generator A visual tool for generating the code for tables in LaTeX
LaTeX Trees Generator A tool for drawing trees in LaTeX
Asymptote A “powerful descriptive vector graphics language” for drawing coordinate-based diagrams
Geogebra A tool for drawing geometric figures
QuickLaTeX A web service for rendering LaTeX on websites

Research Papers

arXiv Access pre-prints of many research papers for free
JSTOR Access journal papers if you have or your institution has a subscription
Mathscinet An online bibliographic database that requires a subscription

Computational Search

WolframAlpha Good for basic computations and visualizations involving standard functions and operations
Magma Software for “computations in algebra, number theory, algebraic geometry and algebraic combinatorics”
Sage A “free open-source mathematics software system”
PARI A computing system for algebra and number theory
Approach0.xyz A LaTeX-based search engine for mathematics

Institutions

Canadian Mathematical Society Host of the Canadian Open and Canadian Mathematical Olympiad
CEMC at the University of Waterloo The Centre for Education in Mathematics and Computing hosts numerous prestigious math contests
American Mathematical Society A society that develops valuable mathematical resources such as LaTeX packages
Mathematical Association of America Host of the sequence of mathematical competitions leading to the USA Mathematical Olympiad
International Mathematical Olympiad Freely access problems from one of the hardest international math competitions for high school students