Browse by Set
Explore famous collections and compilations of unsolved problems
Millennium Prize Problems
Seven problems selected by the Clay Mathematics Institute in 2000, each with a $1,000,000 prize for solution.
Hilbert's 23 Problems
David Hilbert's list of 23 unsolved problems presented at the International Congress of Mathematicians in Paris in 1900.
Ben Green's 100 Open Problems
A collection of 100 open problems in additive combinatorics and related areas, compiled by Ben Green.
DARPA's 23 Mathematical Challenges
Mathematical challenges identified by DARPA to drive fundamental research in mathematics.
Smale's Problems
Steve Smale's list of mathematical problems for the 21st century.
Landau's Problems
Four basic problems about prime numbers posed by Edmund Landau at the 1912 International Congress of Mathematicians.
Hardy-Littlewood Conjectures
A collection of fundamental conjectures on prime numbers, Goldbach-type problems, and Waring's problem from the "Partitio Numerorum" papers (1919-1923) by G.H. Hardy and J.E. Littlewood.
Erdős Problems
A collection of open problems posed by Paul Erdős, one of the most prolific mathematicians of the 20th century. These problems span combinatorics, number theory, graph theory, and analysis.
Richard Guy - A: Prime Numbers
Problems from Chapter A (Prime Numbers) of Richard Guy's "Unsolved Problems in Number Theory", a comprehensive collection of open questions in prime number theory.
Kourovka Notebook - New Problems, Issue 21
New group theory problems from the 21st issue of the Kourovka Notebook, published in 2026.
Kirby's Problems in Low-Dimensional Topology
Problems from Kirby-style notes on low-dimensional topology, including knot theory, 3-manifolds, 4-manifolds, and related invariants.
OpenGarden
Problems imported from the Open Problem Garden collection, using source statements, discussion notes, and subject metadata.