Unsolved Problems
- 2
- A-Sequence
- abc Conjecture
- Ablowitz-Ramani-Segur Conjecture
- Agoh's Conjecture
- Algebraic Period
- Aliquot Sequence
- Almost Perfect Number
- Alon-Tarsi Conjecture
- Alternating Series
- Andrica's Conjecture
- Apex Graph
- Artin's Conjecture
- Aspiring Number
- Baillie-PSW Primality Test
- Ball Triangle Picking
- Barker Code
- Barnette's Conjecture
- Baxter-Hickerson Function
- Beal's Conjecture
- Bell Number
- Benson's Formula
- Beraha Constants
- Berry Conjecture
- Borwein Conjectures
- Bouniakowsky Conjecture
- Braun's Conjecture
- Brocard's Conjecture
- Carmichael's Totient Function Conjecture
- Catalan's Aliquot Sequence Conjecture
- Central Binomial Coefficient
- Central Trinomial Coefficient
- Class Number
- Coin Problem
- Coin Tossing
- Collatz Problem
- Complementary Subspace Problem
- Completely Positive Matrix
- Concurrent Normals Conjecture
- Conference Graph
- Constant Problem
- Costas Array
- Cramér Conjecture
- Cramér-Granville Conjecture
- Cube 3-Compound
- Cube Triangle Picking
- Cubic Nonhamiltonian Graph
- Cycle Double Cover Conjecture
- Cyclic Number
- Cyclic Polygon
- Dark Satanic Mills on a Cloudy Day
- de Grey Graphs
- de Polignac's Conjecture
- Deletable Prime
- Determined by Spectrum
- Disk Triangle Picking
- Domination Root
- Double Mersenne Number
- Earth-Moon Problem
- Eberhart's Conjecture
- Edge-Graceful Graph
- Eight Curve
- Erdős-Ivić Conjecture
- Erdős-Straus Conjecture
- Erdős-Szekeres Conjecture
- Erdős-Turán Conjecture
- Erdős Unit Distance Problem
- Eternity
- Euclid-Mullin Sequence
- Euler's Conjecture
- Euler-Mascheroni Constant
- Euler Square
- Euler's Sum of Powers Conjecture
- Exponential Integral
- Factorial Sums
- Fermat-Catalan Conjecture
- Flint Hills Series
- Forbidden Minor
- Fortunate Prime
- Four Exponentials Conjecture
- Friendly Number
- Friendly Pair
- Fuglede's Conjecture
- Full Reptend Prime
- Gelfand's Question
- Generalized Moore Graph
- Generalized Riemann Hypothesis
- Gilbreath's Conjecture
- Giuga's Conjecture
- Goldbach Conjecture
- Goldbach Partition
- Golomb Ruler
- Gömböc
- Grabarchuk Graph
- Graceful Tree Theorem
- Graph Crossing Number
- Graph Distance Matrix
- Graph Spectrum
- Graph Toughness
- Grimm's Conjecture
- Guy's Conjecture
- H^*-Connected Graph
- Hadamard Matrix
- Hadwiger Conjecture
- Hadwiger-Nelson Problem
- Haemers Conjecture
- Halting Problem
- Happy End Problem
- Harborth Graph
- Hard Square Entropy Constant
- Hardy-Littlewood Conjectures
- Harmonic Series
- Hasse's Conjecture
- Heilbronn Triangle Problem
- Heule Graphs
- Hilbert's Problems
- Hodge Conjecture
- Hoffman-Singleton Theorem
- Holyhedron
- Hyperbolic Knot
- Hyperbolic Octahedron
- Hypercube Graph
- Hypercube Line Picking
- Hypercube Point Picking
- Idoneal Number
- Isomorphic Factorization
- Jacobian Conjecture
- Juggler Sequence
- k-Tuple Conjecture
- Kaplan-Yorke Conjecture
- Khinchin's Constant
- Kimberling Sequence
- Klein Bottle Crossing Number
- Kobon Triangle
- Kreisel Conjecture
- Kronecker-Weber Theorem
- Landau's Problems
- Langlands Program
- Langton's Ant
- Latin Square
- Legendre's Conjecture
- Lehmer's Constant
- Lehmer's Mahler Measure Problem
- Lehmer's Totient Problem
- Levy's Conjecture
- Lichtenbaum-Quillen Conjecture
- Littlewood Conjecture
- Local Density Conjecture
- Log Gamma Function
- Lovász Conjecture
- Madelung Constants
- Magic Square
- Mandelbrot Set
- Markström Graph
- Mastermind
- Matchstick Graph
- Meissner Tetrahedra
- Mersenne Prime
- Mertens Theorem
- Mixon Graphs
- Montgomery-Odlyzko Law
- Montgomery's Pair Correlation Conjecture
- Mrs. Perkins's Quilt
- Multiplicative Persistence
- Net
- New Mersenne Prime Conjecture
- Newman's Conjecture
- Nonhamiltonian Vertex-Transitive Graph
- Normal Number
- NP-Problem
- Octahedral Number
- Octahedron Tetrahedron Picking
- Odd Perfect Number
- Oloid
- Orchard-Planting Problem
- Ore's Conjecture
- P Versus NP Problem
- Padé Conjecture
- Palindromic Number Conjecture
- Parts Graphs
- Percolation Threshold
- Perfect Cuboid
- Perfect Magic Cube
- Perfect Number
- Perfectly Hamiltonian Graph
- Pi Formulas
- Pillai's Conjecture
- Pollock's Conjecture
- Pósa's Conjecture
- Positive Eigenvalued Matrix
- Powerful Number
- Prime Array
- Prime Gaps
- Prime Power Conjecture
- Projective Plane
- Quartic Nonhamiltonian Graph
- Quasiperfect Number
- Quillen-Lichtenbaum Conjecture
- Quintic Nonhamiltonian Graph
- Rabin-Miller Strong Pseudoprime Test
- Random Close Packing
- Rational Distance Problem
- Rational Number
- Rectilinear Crossing Number
- Riemann Hypothesis
- Riemann Zeta Function
- Robin's Theorem
- Ruth-Aaron Pair
- Sausage Conjecture
- Schanuel's Conjecture
- Schinzel's Hypothesis
- Scholz Conjecture
- Selfridge's Conjecture
- Sendov Conjecture
- Seymour Conjecture
- Shanks' Conjecture
- Shannon Capacity
- Shephard's Conjecture
- Sierpiński's Composite Number Theorem
- Sierpiński Number of the Second Kind
- Simon's Problems
- Simplex Simplex Picking
- Smale's Problems
- Smallest Cubic Crossing Number Graph
- Smallest Quartic Crossing Number Graph
- Smarandache Function
- Smarandache Prime
- Social Golfer Problem
- Solitary Number
- Sophie Germain Prime
- Sparse Ruler
- Sphere Packing
- Sphere Tetrahedron Picking
- Spherical Code
- Square Point Picking
- Strong Pseudoprime
- Strongly Regular Graph
- Swinnerton-Dyer Conjecture
- Szpiro's Conjecture
- Tait's Knot Conjectures
- Tanc Function
- Taylor's Condition
- Ternary
- Tetrahedral Number
- Tetrahedron Circumscribing
- Tetrahedron Triangle Picking
- Thurston Elliptization Conjecture
- Thurston's Geometrization Conjecture
- Toroidal Crossing Number
- Totient Function
- Totient Valence Function
- Tower of Hanoi
- Traveling Salesman Problem
- Triangle Triangle Picking
- Trinomial Coefficient
- Twin Prime Conjecture
- Twin Primes
- Ulam's Conjecture
- Unfolding
- Uniformity Conjecture
- Union-Closed Sets Conjecture
- Uniquely Pancyclic Graph
- Unistable Polyhedron
- Universal Turing Machine
- Unsolved Problems
- Untouchable Number
- van Cleemput-Zamfirescu Graphs
- Vizing Conjecture
- Vojta's Conjecture
- Wagstaff's Conjecture
- Wagstaff Prime
- Wall-Sun-Sun Prime
- Waring's Prime Number Conjecture
- Weil Conjectures
- Weird Number
- Wichmann Ruler
- Wilson Prime
- Wolstenholme Prime
- Zarankiewicz's Conjecture
- Znám's Problem