Math
For math students and problem solvers.
Communities for math students, enthusiasts, and professionals covering everything from calculus help to higher-level pure and applied mathematics. Reddit has large communities for homework help and recreational math, with Discord servers serving students and dedicated forums for specific branches of the discipline.
Communities
A question and answer site for people studying math at any level and professionals in related fields. Part of the Stack Exchange network.
This subreddit is for discussion of mathematical links and questions.
Art of Problem Solving creates educational materials for motivated students in grades 2–12. The company's books, classes, and online resources help students become creative, successful problem solvers. The website contains a community forum that is available to all that have math questions.
This is a subreddit for discussion on all things dealing with statistical theory, software, and application. We welcome all researchers, students, professionals, and enthusiasts looking to be a part of an online statistics community.

An active community for math enthusiasts, focused on the appreciation of mathematics, homework help, and teaching new concepts. Features channels for various levels of math.
Post all of your math-learning resources here. Questions, no matter how basic, will be answered (to the best ability of the online subscribers).
MathOverflow is a question and answer site for professional mathematicians. Anybody can ask a question. Anybody can answer. The best answers are voted up and rise to the top.

Welcome to r/AskStatistics. Ask away!

Number Theory is a mathematical study of the axiomatic properties of positive integers including powers of integers, squares, cubes, triangular, factorial, Fibonacci, composite, prime, perfect, Mersenne, Fermat, Ramanujan, factors, Pisot, social, deficient, abundant, Pickover, Batrachian and modular forms. This group is formed to advance the use of number theory in physics, chaos theory and fractal theory as well. Dirichlet and zeta functions as they apply to the theory of numbers will be discussed. Both cyclotomic and subcyclotomic numbers are also of great interest in Pisot and metal means discussions. We will welcome open discussions and new developments in number theory.

Math education! r/matheducation is focused on mathematics pedagogy (the teaching of). Please avoid posts that are related to homework or other "How do I solve this?" type questions. There should be an emphasis on usefulness (such as good internet resources or ideas for how to teach a concept).

Mathematics, Chess Problems, ChessBoard Puzzles, Math Chess and unusual aspects of the chess world...

Welcome to Cosmos Domain! We invite you to explore and learn with us! Join our server for various topics like math, physics, astronomy, biology, chemistry, and more STEM subjects!

The Mathematical Association of America is the world’s largest community of mathematicians, students, and enthusiasts. We further the understanding of our world through mathematics because mathematics drives society and shapes our lives.
Mathematics is concerned with numbers, data, quantity, structure, space, models, and change. Founded in 2005, Math Help Forum is dedicated to free math help and math discussions, and our math community welcomes students, teachers, educators, professors, mathematicians, engineers, and scientists.