List of unsolved problems in mathematics
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Since the Renaissance, every century has seen the solution of more mathematical problems than the century before, and yet many mathematical problems, both major and minor, still remain unsolved.^{[1]} Prizes are often awarded for the solution to a longstanding problem, and lists of unsolved problems (such as the list of Millennium Prize Problems) receive considerable attention. Unsolved problems remain in multiple domains, including physics, computer science, algebra, additive and algebraic number theories, analysis, combinatorics, algebraic, discrete and Euclidean geometries, graph, group, model, number, set and Ramsey theories, dynamical systems, partial differential equations, and miscellaneous unsolved problems.
Contents
 1 Lists of unsolved problems in mathematics
 2 Unsolved problems
 3 Problems solved since 1995
 4 References
 5 Further reading
 6 External links
Lists of unsolved problems in mathematics
Over the course of time, several lists of unsolved mathematical problems have appeared.
List  Number of problems  Proposed by  Proposed in 

Hilbert's problems^{[2]}  23  David Hilbert  1900 
Landau's problems^{[3]}  4  Edmund Landau  1912 
Taniyama's problems^{[4]}  36  Yutaka Taniyama  1955 
Thurston's 24 questions^{[5]}^{[6]}  24  William Thurston  1982 
Smale's problems  18  Stephen Smale  1998 
Millennium Prize problems  7  Clay Mathematics Institute  2000 
Unsolved Problems on Mathematics for the 21st Century^{[7]}  22  Jair Minoro Abe, Shotaro Tanaka  2001 
DARPA's math challenges^{[8]}^{[9]}  23  DARPA  2007 
Millennium Prize Problems
Of the original seven Millennium Prize Problems set by the Clay Mathematics Institute in 2000, six have yet to be solved, as of 2017:^{[10]}
 P versus NP
 Hodge conjecture
 Riemann hypothesis
 Yang–Mills existence and mass gap
 Navier–Stokes existence and smoothness
 Birch and SwinnertonDyer conjecture
The seventh problem, the Poincaré conjecture, has been solved.^{[11]} The smooth fourdimensional Poincaré conjecture—that is, whether a fourdimensional topological sphere can have two or more inequivalent smooth structures—is still unsolved.^{[12]}
Unsolved problems
Algebra
 Homological conjectures in commutative algebra
 Hilbert's sixteenth problem
 Hilbert's fifteenth problem
 Hadamard conjecture
 Jacobson's conjecture
 Existence of perfect cuboids and associated cuboid conjectures
 Zauner's conjecture: existence of SICPOVMs in all dimensions
 Wild Problem: Classification of pairs of n×n matrices under simultaneous conjugation and problems containing it such as a lot of classification problems
 Köthe conjecture
 Birch–Tate conjecture
 Serre's conjecture II
 Bombieri–Lang conjecture
 Farrell–Jones conjecture
 Bost conjecture
 Uniformity conjecture
 Kaplansky's conjecture
 Kummer–Vandiver conjecture
 Serre's multiplicity conjectures
 Pierce–Birkhoff conjecture
 Eilenberg–Ganea conjecture
 Green's conjecture
 Grothendieck–Katz pcurvature conjecture
 Sendov's conjecture
Algebraic geometry
 Bass conjecture
 Deligne conjecture
 Fröberg conjecture
 Fujita conjecture
 Hartshorne conjectures
 The Jacobian conjecture
 Manin conjecture
 Nakai conjecture
 Resolution of singularities in characteristic p
 Standard conjectures on algebraic cycles
 Section conjecture
 Tate conjecture
 Virasoro conjecture
 Zariski multiplicity conjecture
Analysis
 Schanuel's conjecture and four exponentials conjecture
 Lehmer's conjecture
 Pompeiu problem
 Are (the Euler–Mascheroni constant), π + e, π − e, πe, π/e, π^{e}, π^{√2}, π^{π}, e^{π2}, ln π, 2^{e}, e^{e}, Catalan's constant or Khinchin's constant rational, algebraic irrational, or transcendental? What is the irrationality measure of each of these numbers?^{[13]}^{[14]}^{[15]}
 Khabibullin’s conjecture on integral inequalities
 Hilbert's thirteenth problem
 Vitushkin's conjecture
Combinatorics
 Number of magic squares (sequence A006052 in the OEIS)
 Number of magic tori (sequence A270876 in the OEIS)
 Finding a formula for the probability that two elements chosen at random generate the symmetric group
 Finding a formula for the number of selfavoiding random walks with a given number of steps.
 Frankl's unionclosed sets conjecture: for any family of sets closed under sums there exists an element (of the underlying space) belonging to half or more of the sets
 The lonely runner conjecture: if runners with pairwise distinct speeds run round a track of unit length, will every runner be "lonely" (that is, be at least a distance from each other runner) at some time?
 Singmaster's conjecture: is there a finite upper bound on the multiplicities of the entries greater than 1 in Pascal's triangle?
 The 1/3–2/3 conjecture: does every finite partially ordered set that is not totally ordered contain two elements x and y such that the probability that x appears before y in a random linear extension is between 1/3 and 2/3?
 unicity conjecture for Markov numbers
 Give a combinatorial interpretation of the Kronecker coefficients.
Discrete geometry
 Solving the happy ending problem for arbitrary
 Finding matching upper and lower bounds for ksets and halving lines
 The Hadwiger conjecture on covering ndimensional convex bodies with at most 2^{n} smaller copies
 The Kobon triangle problem on triangles in line arrangements
 The McMullen problem on projectively transforming sets of points into convex position
 Ulam's packing conjecture about the identity of the worstpacking convex solid
 Filling area conjecture
 Hopf conjecture
 Kakeya conjecture
 Kissing number problem for dimensions other than 1, 2, 3, 4, 8 and 24
 How many unit distances can be determined by a set of n points? (see Counting unit distances)
Euclidean geometry
 The einstein problem – does there exist a twodimensional shape that forms the prototile for an aperiodic tiling, but not for any periodic tiling?^{[16]}
 Inscribed square problem – does every Jordan curve have an inscribed square?^{[17]}
 Moser's worm problem – what is the smallest area of a shape that can cover every unitlength curve in the plane?^{[18]}
 The moving sofa problem – what is the largest area of a shape that can be maneuvered through a unitwidth Lshaped corridor?^{[19]}
 Shephard's problem (a.k.a. Dürer's conjecture) – does every convex polyhedron have a net?^{[20]}
 The Thomson problem – what is the minimum energy configuration of N particles bound to the surface of a unit sphere that repel each other with a 1/r potential (or any potential in general)?
 Pentagonal tiling – 15 types of convex pentagons are known to monohedrally tile the plane, and it is not known whether this list is complete.^{[21]}
 Falconer's conjecture
 gconjecture
 Circle packing in an equilateral triangle
 Circle packing in an isosceles right triangle
 Lebesgue's universal covering problem – what is the convex shape in the plane of least area which provides an isometric cover for any shape of diameter one?
 Bellman's lost in a forest problem – for a given shape of forest find the shortest escape path which will intersect the edge of the forest at some point for any given starting point and direction inside the forest.
 Find the complete set of uniform 5polytopes^{[22]}
 Covering problem of Rado
 The strong bellows conjecture – must the Dehn invariant of a selfintersection free flexible polyhedron stay constant as it flexes?
Dynamical systems
 Lyapunov's second method for stability – For what classes of ODEs, describing dynamical systems, does the Lyapunov’s second method formulated in the classical and canonically generalized forms define the necessary and sufficient conditions for the (asymptotical) stability of motion?
 Furstenberg conjecture – Is every invariant and ergodic measure for the action on the circle either Lebesgue or atomic?
 Margulis conjecture — Measure classification for diagonalizable actions in higherrank groups
 MLC conjecture – Is the Mandelbrot set locally connected?
 Weinstein conjecture – Does a regular compact contact type level set of a Hamiltonian on a symplectic manifold carry at least one periodic orbit of the Hamiltonian flow?
 Is every reversible cellular automaton in three or more dimensions locally reversible?^{[23]}
 Many problems concerning an outer billiard, for example show that outer billiards relative to almost every convex polygon has unbounded orbits.
Graph theory
Paths and cycles in graphs
 Barnette's conjecture that every cubic bipartite threeconnected planar graph has a Hamiltonian cycle^{[24]}
 Chvátal's toughness conjecture, that there is a number t such that every ttough graph is Hamiltonian^{[25]}
 The cycle double cover conjecture that every bridgeless graph has a family of cycles that includes each edge twice^{[26]}
 The Erdős–Gyárfás conjecture on cycles with poweroftwo lengths in cubic graphs^{[27]}
 The linear arboricity conjecture on decomposing graphs into disjoint unions of paths according to their maximum degree^{[28]}
 The Lovász conjecture on Hamiltonian paths in symmetric graphs^{[29]}
Graph coloring and labeling
 The Erdős–Faber–Lovász conjecture on coloring unions of cliques^{[30]}
 The Hadwiger conjecture relating coloring to clique minors^{[31]}
 The Hadwiger–Nelson problem on the chromatic number of unit distance graphs^{[32]}
 Hedetniemi's conjecture on the chromatic number of tensor products of graphs^{[33]}
 Jaeger's Petersencoloring conjecture that every bridgeless cubic graph has a cyclecontinuous mapping to the Petersen graph^{[34]}
 The list coloring conjecture that, for every graph, the list chromatic index equals the chromatic index^{[35]}
 The Ringel–Kotzig conjecture on graceful labeling of trees^{[36]}
 The total coloring conjecture of Behzad and Vizing that the total chromatic number is at most two plus the maximum degree^{[37]}
Graph drawing
 The Albertson conjecture that the crossing number can be lowerbounded by the crossing number of a complete graph with the same chromatic number^{[38]}
 The Blankenship–Oporowski conjecture on the book thickness of subdivisions^{[39]}
 Conway's thrackle conjecture^{[40]}
 Harborth's conjecture that every planar graph can be drawn with integer edge lengths^{[41]}
 Negami's conjecture on projectiveplane embeddings of graphs with planar covers^{[42]}
 The strong Papadimitriou–Ratajczak conjecture that every polyhedral graph has a convex greedy embedding^{[43]}
 Turán's brick factory problem – Is there a drawing of any complete bipartite graph with fewer crossings than the number given by Zarankiewicz?^{[44]}
 Universal point sets of subquadratic size for planar graphs^{[45]}
Miscellaneous graph theory
 The Erdős–Hajnal conjecture on large cliques or independent sets in graphs with a forbidden induced subgraph^{[46]}
 The implicit graph conjecture on the existence of implicit representations for slowlygrowing hereditary families of graphs^{[47]}
 Jørgensen's conjecture that every 6vertexconnected K_{6}minorfree graph is an apex graph^{[48]}
 Deriving a closedform expression for the percolation threshold values, especially (square site)
 Does a Moore graph with girth 5 and degree 57 exist?
 What is the largest possible pathwidth of an nvertex cubic graph?
 The reconstruction conjecture and new digraph reconstruction conjecture on whether a graph is uniquely determined by its vertexdeleted subgraphs.
 Sumner's conjecture: does every vertex tournament contain as a subgraph every vertex oriented tree?^{[49]}
 Tutte's conjectures that every bridgeless graph has a nowherezero 5flow and every Petersenminorfree bridgeless graph has a nowherezero 4flow
 Vizing's conjecture on the domination number of cartesian products of graphs^{[50]}
Group theory
 Is every finitely presented periodic group finite?
 The inverse Galois problem: is every finite group the Galois group of a Galois extension of the rationals?
 For which positive integers m, n is the free Burnside group B(m,n) finite? In particular, is B(2, 5) finite?
 Is every group surjunctive?
 Andrews–Curtis conjecture
 Herzog–Schönheim conjecture
 Does generalized moonshine exist?
Model theory
 Vaught's conjecture
 The Cherlin–Zilber conjecture: A simple group whose firstorder theory is stable in is a simple algebraic group over an algebraically closed field.
 The Main Gap conjecture, e.g. for uncountable first order theories, for AECs, and for saturated models of a countable theory.^{[51]}
 Determine the structure of Keisler's order^{[52]}^{[53]}
 The stable field conjecture: every infinite field with a stable firstorder theory is separably closed.
 Is the theory of the field of Laurent series over decidable? of the field of polynomials over ?
 (BMTO) Is the Borel monadic theory of the real order decidable? (MTWO) Is the monadic theory of wellordering consistently decidable?^{[54]}
 The Stable Forking Conjecture for simple theories^{[55]}
 For which number fields does Hilbert's tenth problem hold?
 Assume K is the class of models of a countable first order theory omitting countably many types. If K has a model of cardinality does it have a model of cardinality continuum?^{[56]}
 Shelah's eventual Categority conjecture: For every cardinal there exists a cardinal such that If an AEC K with LS(K)<= is categorical in a cardinal above then it is categorical in all cardinals above .^{[51]}^{[57]}
 Shelah's categoricity conjecture for : If a sentence is categorical above the Hanf number then it is categorical in all cardinals above the Hanf number.^{[51]}
 Is there a logic L which satisfies both the Beth property and Δinterpolation, is compact but does not satisfy the interpolation property?^{[58]}
 If the class of atomic models of a complete first order theory is categorical in the , is it categorical in every cardinal?^{[59]}^{[60]}
 Is every infinite, minimal field of characteristic zero algebraically closed? (minimal = no proper elementary substructure)
 Kueker's conjecture^{[61]}
 Does there exist an ominimal first order theory with a transexponential (rapid growth) function?
 Lachlan's decision problem
 Does a finitely presented homogeneous structure for a finite relational language have finitely many reducts?
 Do the Henson graphs have the finite model property? (e.g. trianglefree graphs)
 The universality problem for Cfree graphs: For which finite sets C of graphs does the class of Cfree countable graphs have a universal member under strong embeddings?^{[62]}
 The universality spectrum problem: Is there a firstorder theory whose universality spectrum is minimum?^{[63]}
Number theory
General
 Grand Riemann hypothesis

n conjecture
 abc conjecture (Proof claimed in 2012, currently under review.)
 Hilbert's ninth problem
 Hilbert's eleventh problem
 Hilbert's twelfth problem
 Carmichael's totient function conjecture
 Erdős–Straus conjecture
 Pillai's conjecture
 Hall's conjecture
 Lindelöf hypothesis
 Montgomery's pair correlation conjecture
 Hilbert–Pólya conjecture
 Grimm's conjecture
 Leopoldt's conjecture
 Do any odd perfect numbers exist?
 Are there infinitely many perfect numbers?
 Do quasiperfect numbers exist?
 Do any odd weird numbers exist?
 Do any Lychrel numbers exist?
 Is 10 a solitary number?
 Catalan–Dickson conjecture on aliquot sequences
 Do any Taxicab(5, 2, n) exist for n > 1?
 Brocard's problem: existence of integers, (n,m), such that n! + 1 = m^{2} other than n = 4, 5, 7
 Beilinson conjecture
 Littlewood conjecture
 Szpiro's conjecture
 Vojta's conjecture
 Goormaghtigh conjecture
 Congruent number problem (a corollary to Birch and SwinnertonDyer conjecture, per Tunnell's theorem)
 Lehmer's totient problem: if φ(n) divides n − 1, must n be prime?
 Are there infinitely many amicable numbers?
 Are there any pairs of amicable numbers which have opposite parity?
 Are there any pairs of relatively prime amicable numbers?
 Are there infinitely many betrothed numbers?
 Are there any pairs of betrothed numbers which have same parity?
 The Gauss circle problem – how far can the number of integer points in a circle centered at the origin be from the area of the circle?
 Piltz divisor problem, especially Dirichlet's divisor problem
 Exponent pair conjecture
 Is π a normal number (its digits are "random")?^{[64]}
 CasasAlvero conjecture
 Sato–Tate conjecture
 Find value of De Bruijn–Newman constant
 Which integers can be written as the sum of three perfect cubes?^{[65]}
 Erdős–Moser problem: is 1^{1} + 2^{1} = 3^{1} the only solution to the Erdős–Moser equation?
Additive number theory
 Beal's conjecture
 Fermat–Catalan conjecture
 Goldbach's conjecture
 The values of g(k) and G(k) in Waring's problem
 Collatz conjecture (3n + 1 conjecture)
 Lander, Parkin, and Selfridge conjecture
 Gilbreath's conjecture
 Erdős conjecture on arithmetic progressions
 Erdős–Turán conjecture on additive bases
 Pollock octahedral numbers conjecture
 Skolem problem
 Determine growth rate of r_{k}(N) (see Szemerédi's theorem)
 Minimum overlap problem
Algebraic number theory
 Are there infinitely many real quadratic number fields with unique factorization (Class number problem)?
 Characterize all algebraic number fields that have some power basis.
 Stark conjectures (including Brumer–Stark conjecture)
 Kummer–Vandiver conjecture
Combinatorial number theory
 Singmaster's conjecture: Is there a finite upper bound on the number of times that a number other than 1 can appear in Pascal's triangle?
Prime numbers
 Catalan's Mersenne conjecture
 Agoh–Giuga conjecture
 The Gaussian moat problem: is it possible to find an infinite sequence of distinct Gaussian prime numbers such that the difference between consecutive numbers in the sequence is bounded?
 New Mersenne conjecture
 Erdős–Mollin–Walsh conjecture
 Are there infinitely many prime quadruplets?
 Are there infinitely many cousin primes?
 Are there infinitely many sexy primes?
 Are there infinitely many Mersenne primes (Lenstra–Pomerance–Wagstaff conjecture); equivalently, infinitely many even perfect numbers?
 Are there infinitely many Wagstaff primes?
 Are there infinitely many Sophie Germain primes?
 Are there infinitely many Pierpont primes?
 Are there infinitely many regular primes, and if so is their relative density ?
 For any given integer b which is not a perfect power and not of the form −4k^{4} for integer k, are there infinitely many repunit primes to base b?
 Are there infinitely many Cullen primes?
 Are there infinitely many Woodall primes?
 Are there infinitely many palindromic primes to every base?
 Are there infinitely many Fibonacci primes?
 Are there infinitely many Lucas primes?
 Are there infinitely many Pell primes?
 Are there infinitely many Newman–Shanks–Williams primes?
 Are all Mersenne numbers of prime index squarefree?
 Are there infinitely many Wieferich primes?
 Are there any Wieferich primes in base 47?
 Are there any composite c satisfying 2^{c − 1} ≡ 1 (mod c^{2})?
 For any given integer a > 0, are there infinitely many primes p such that a^{p − 1} ≡ 1 (mod p^{2})?^{[66]}
 Can a prime p satisfy 2^{p − 1} ≡ 1 (mod p^{2}) and 3^{p − 1} ≡ 1 (mod p^{2}) simultaneously?^{[67]}
 Are there infinitely many Wilson primes?
 Are there infinitely many Wolstenholme primes?
 Are there any Wall–Sun–Sun primes?
 Is every Fermat number 2^{2n} + 1 composite for ?
 Are all Fermat numbers squarefree?
 For any given integer a which is not a square and does not equal to −1, are there infinitely many primes with a as a primitive root?
 Artin's conjecture on primitive roots
 Is 78,557 the lowest Sierpiński number (socalled Selfridge's conjecture)?
 Is 509,203 the lowest Riesel number?
 Fortune's conjecture (that no Fortunate number is composite)
 Landau's problems
 Feit–Thompson conjecture
 Does every prime number appear in the Euclid–Mullin sequence?
 Does the converse of Wolstenholme's theorem hold for all natural numbers?
 Elliott–Halberstam conjecture
 Problems associated to Linnik's theorem
 Find the smallest Skewes' number
Partial differential equations
 Regularity of solutions of Vlasov–Maxwell equations
 Regularity of solutions of Euler equations
Ramsey theory
 The values of the Ramsey numbers, particularly
 The values of the Van der Waerden numbers
 Erdős–Burr conjecture
Set theory
 The problem of finding the ultimate core model, one that contains all large cardinals.
 If ℵ_{ω} is a strong limit cardinal, then 2^{ℵω} < ℵ_{ω1} (see Singular cardinals hypothesis). The best bound, ℵ_{ω4}, was obtained by Shelah using his pcf theory.
 Woodin's Ωhypothesis.
 Does the consistency of the existence of a strongly compact cardinal imply the consistent existence of a supercompact cardinal?
 (Woodin) Does the Generalized Continuum Hypothesis below a strongly compact cardinal imply the Generalized Continuum Hypothesis everywhere?
 Does there exist a Jónsson algebra on ℵ_{ω}?
 Without assuming the axiom of choice, can a nontrivial elementary embedding V→V exist?
 Does the Generalized Continuum Hypothesis entail for every singular cardinal ?
 Does the Generalized Continuum Hypothesis imply the existence of an ℵ_{2}Suslin tree?
Other
 List of unsolved problems in statistics
 List of unsolved problems in computer science
 Problems in loop theory and quasigroup theory
 Problems in Latin squares
 Invariant subspace problem
 Kaplansky's conjectures on groups rings
 Painlevé conjecture
 Dixmier conjecture
 Baum–Connes conjecture
 Novikov conjecture
 Prove Turing completeness for all unique elementary cellular automaton
 Generalized star height problem
 Assorted sphere packing problems, e.g. the densest irregular hypersphere packings
 Closed curve problem: Find (explicit) necessary and sufficient conditions that determine when, given two periodic functions with the same period, the integral curve is closed.^{[68]}
 Keating–Snaith conjecture
 Kung–Traub conjecture
 Atiyah conjecture on configurations
 Toeplitz' conjecture (open since 1911)
 Carathéodory conjecture
 Church–Turing thesis
 Weightmonodromy conjecture
 Berry–Tabor conjecture
 Birkhoff conjecture
 Guralnick–Thompson conjecture
 Hilbert–Smith conjecture
 MNOP conjecture
 Mazur's conjectures
 Rendezvous problem
 Scholz conjecture
 Nirenberg–Treves conjecture
 Quantum unique ergodicity conjecture
 Density hypothesis
 Zhou conjecture
 Borel conjecture
 Zeeman conjecture
 Erdös–Ulam problem
Problems solved since 1995
 Boolean Pythagorean triples problem (Marijn Heule, Oliver Kullmann, Victor Marek, 2016)^{[69]}
 Babai's problem (Problem 3.3 in "Spectra of Cayley graphs") (A. Abdollahi, M. Zallaghi, 2015)^{[70]}
 Main conjecture in Vinogradov's meanvalue theorem (Jean Bourgain, Ciprian Demeter, Larry Guth, 2015)^{[71]}
 Erdős discrepancy problem (Terence Tao, 2015)^{[72]}
 Umbral moonshine conjecture (John F. R. Duncan, Michael J. Griffin, Ken Ono, 2015)^{[73]}
 Anderson conjecture (Cheeger, Naber, 2014)^{[74]}
 Goldbach's weak conjecture (Harald Helfgott, 2013)^{[75]}^{[76]}^{[77]}
 Kadison–Singer problem (Adam Marcus, Daniel Spielman and Nikhil Srivastava, 2013)^{[78]}^{[79]} (and the Feichtinger's conjecture, Anderson’s paving conjectures, Weaver’s discrepancy theoretic and conjectures, BourgainTzafriri conjecture and conjecture)
 Virtual Haken conjecture (Agol, Groves, Manning, 2012)^{[80]} (and by work of Wise also virtually fibered conjecture)
 Hsiang–Lawson's conjecture (Brendle, 2012)^{[81]}
 Willmore conjecture (Fernando Codá Marques and André Neves, 2012)^{[82]}
 Ehrenpreis conjecture (Kahn, Markovic, 2011)^{[83]}
 Hanna Neumann conjecture (Mineyev, 2011)^{[84]}
 Bloch–Kato conjecture (Voevodsky, 2011)^{[85]} (and Quillen–Lichtenbaum conjecture and by work of Geisser and Levine (2001) also Beilinson–Lichtenbaum conjecture^{[86]}^{[87]}^{[88]})
 Erdős distinct distances problem (Larry Guth, Netz Hawk Katz, 2011)^{[89]}
 Density theorem (Namazi, Souto, 2010)^{[90]}
 Hirsch conjecture (Francisco Santos Leal, 2010)^{[91]}^{[92]}
 Sidon set problem (J. Cilleruelo, I. Ruzsa and C. Vinuesa, 2010)^{[93]}
 Atiyah conjecture (Austin, 2009)^{[94]}
 Kauffman–Harary conjecture (Matmann, Solis, 2009)^{[95]}
 Surface subgroup conjecture (Kahn, Markovic, 2009)^{[96]}
 Scheinerman's conjecture (Jeremie Chalopin and Daniel Gonçalves, 2009)^{[97]}
 Full classification of finite simple groups (Harada, Solomon, 2008)
 Geometrization conjecture (proof was completed by Morgan and Tian in 2008^{[98]} and it is based mostly on work of Grigori Perelman, 2002)^{[99]}
 Serre's modularity conjecture (Chandrashekhar Khare and JeanPierre Wintenberger, 2008)^{[100]}^{[101]}^{[102]}
 Heterogeneous tiling conjecture (squaring the plane) (Frederick V. Henle and James M. Henle, 2008)^{[103]}
 Erdős–Menger conjecture (Aharoni, Berger 2007)^{[104]}
 Road coloring conjecture (Avraham Trahtman, 2007)^{[105]}
 The angel problem (Various independent proofs, 2006)^{[106]}^{[107]}^{[108]}^{[109]}
 Lax conjecture (Lewis, Parrilo, Ramana, 2005)^{[110]}
 The Langlands–Shelstad fundamental lemma (Ngô Bảo Châu and Gérard Laumon, 2004)^{[111]}
 Tameness conjecture and Ahlfors measure conjecture (Ian Agol, 2004)^{[112]}
 Robertson–Seymour theorem (Robertson, Seymour, 2004)^{[113]}
 Stanley–Wilf conjecture (Gábor Tardos and Adam Marcus, 2004)^{[114]} (and also Alon–Friedgut conjecture)
 Green–Tao theorem (Ben J. Green and Terence Tao, 2004)^{[115]}
 Ending lamination theorem (Jeffrey F. Brock, Richard D. Canary, Yair N. Minsky, 2004)^{[116]}
 Carpenter's rule problem (Connelly, Demaine, Rote, 2003)^{[117]}
 Cameron–Erdős conjecture (Ben J. Green, 2003, Alexander Sapozhenko, 2003)^{[118]}^{[119]}
 Milnor conjecture (Vladimir Voevodsky, 2003)^{[120]}
 Kemnitz's conjecture (Reiher, 2003, di Fiore, 2003)^{[121]}
 Nagata's conjecture (Shestakov, Umirbaev, 2003)^{[122]}
 Kirillov's conjecture (Baruch, 2003)^{[123]}
 Poincaré conjecture (Grigori Perelman, 2002)^{[99]}
 Strong perfect graph conjecture (Maria Chudnovsky, Neil Robertson, Paul Seymour and Robin Thomas, 2002)^{[124]}
 Kouchnirenko’s conjecture (Haas, 2002)^{[125]}
 Vaught conjecture (Knight, 2002)^{[126]}
 Double bubble conjecture (Hutchings, Morgan, Ritoré, Ros, 2002)^{[127]}
 Catalan's conjecture (Preda Mihăilescu, 2002)^{[128]}
 n! conjecture (Haiman, 2001)^{[129]} (and also Macdonald positivity conjecture)
 Kato's conjecture (Auscher, Hofmann, Lacey, McIntosh and Tchamitchian, 2001)^{[130]}
 Deligne's conjecture on 1motives (Luca BarbieriViale, Andreas Rosenschon, Morihiko Saito, 2001)^{[131]}
 Modularity theorem (Breuil, Conrad, Diamond and Taylor, 2001)^{[132]}
 Erdős–Stewart conjecture (Florian Luca, 2001)^{[133]}
 Berry–Robbins problem (Atiyah, 2000)^{[134]}
 Erdős–Graham problem (Croot, 2000)^{[135]}
 Honeycomb conjecture (Thomas Hales, 1999)^{[136]}
 Gradient conjecture (Krzysztof Kurdyka, Tadeusz Mostowski, Adam Parusinski, 1999)^{[137]}
 Bogomolov conjecture (Emmanuel Ullmo, 1998, ShouWu Zhang, 1998)^{[138]}^{[139]}
 Lafforgue's theorem (Laurent Lafforgue, 1998)^{[140]}
 Kepler conjecture (Ferguson, Hales, 1998)^{[141]}
 Dodecahedral conjecture (Hales, McLaughlin, 1998)^{[142]}
 Ganea conjecture (Iwase, 1997)^{[143]}
 Torsion conjecture (Merel, 1996)^{[144]}
 Harary's conjecture (Chen, 1996)^{[145]}
 Fermat's Last Theorem (Andrew Wiles and Richard Taylor, 1995)^{[146]}^{[147]}
References
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Further reading
Books discussing recently solved problems^{[needs update]}
 Singh, Simon (2002). Fermat's Last Theorem. Fourth Estate. ISBN 1841157910.
 O'Shea, Donal (2007). The Poincaré Conjecture. Penguin. ISBN 9781846140129.
 Szpiro, George G. (2003). Kepler's Conjecture. Wiley. ISBN 0471086010.
 Ronan, Mark (2006). Symmetry and the Monster. Oxford. ISBN 0192807226.
Books discussing unsolved problems
 Fan Chung; Graham, Ron (1999). Erdos on Graphs: His Legacy of Unsolved Problems. AK Peters. ISBN 156881111X.
 Croft, Hallard T.; Falconer, Kenneth J.; Guy, Richard K. (1994). Unsolved Problems in Geometry. Springer. ISBN 0387975063.
 Guy, Richard K. (2004). Unsolved Problems in Number Theory. Springer. ISBN 0387208607.
 Klee, Victor; Wagon, Stan (1996). Old and New Unsolved Problems in Plane Geometry and Number Theory. The Mathematical Association of America. ISBN 0883853159.
 Du Sautoy, Marcus (2003). The Music of the Primes: Searching to Solve the Greatest Mystery in Mathematics. Harper Collins. ISBN 0060935588.
 Derbyshire, John (2003). Prime Obsession: Bernhard Riemann and the Greatest Unsolved Problem in Mathematics. Joseph Henry Press. ISBN 0309085497.
 Devlin, Keith (2006). The Millennium Problems – The Seven Greatest Unsolved* Mathematical Puzzles Of Our Time. Barnes & Noble. ISBN 9780760786598.
 Blondel, Vincent D.; Megrestski, Alexandre (2004). Unsolved problems in mathematical systems and control theory. Princeton University Press. ISBN 0691117489.
 Lizhen Ji, [various]; YatSun Poon, ShingTung Yau (2013). Open Problems and Surveys of Contemporary Mathematics (volume 6 in the Surveys in Modern Mathematics series) (Surveys of Modern Mathematics). International Press of Boston. ISBN 1571462783.
 Waldschmidt, Michel (2004). "Open Diophantine Problems" (PDF). Moscow Mathematical Journal. 4 (1): 245–305. ISSN 16093321. Zbl 1066.11030.
 Mazurov, V. D.; Khukhro, E. I. (1 Jun 2015). "Unsolved Problems in Group Theory. The Kourovka Notebook. No. 18 (English version)". arXiv:1401.0300v6.
 Derbyshire, John (2003). Prime Obsession. The Joseph Henry Press. ISBN 0309085497.
External links
 24 Unsolved Problems and Rewards for them
 List of links to unsolved problems in mathematics, prizes and research
 Open Problem Garden The collection of open problems in mathematics build on the principle of user editable ("wiki") site
 AIM Problem Lists
 Unsolved Problem of the Week Archive. MathPro Press.
 Ball, John M. "Some Open Problems in Elasticity" (PDF).
 Constantin, Peter. "Some open problems and research directions in the mathematical study of fluid dynamics" (PDF).
 Serre, Denis. "Five Open Problems in Compressible Mathematical Fluid Dynamics" (PDF).
 Unsolved Problems in Number Theory, Logic and Cryptography
 200 open problems in graph theory
 The Open Problems Project (TOPP), discrete and computational geometry problems
 Kirby's list of unsolved problems in lowdimensional topology
 Erdös' Problems on Graphs
 A List of Approachable Open Problems in Knot Theory
 Unsolved Problems in Virtual Knot Theory and Combinatorial Knot Theory
 Open problems from the 12th International Conference on Fuzzy Set Theory and Its Applications
 List of open problems in inner model theory
 Aizenman, Michael. "Open Problems in Mathematical Physics".
 15 Problems in Mathematical Physics