All Fun Facts

There are currently 203 Fun Fact files. You can also see a list of recently added Fun Facts.

• e is irrational
• All Horses are the Same Color
• All Numbers are Interesting
• Ants on a Stick
• Arclength Surprise
• Are Coins Fair?
• Area of a Circle or Regular Polygon
• Area of a Hyperbolic Wedge
• Area of an Ellipse
• Arrow's Impossibility Theorem
• Banach-Tarski Paradox
• Behold! the Pythagorean Theorem
• Bike with Square Wheels
• Binary Card Trick
• Birthday Problem
• Borsuk-Ulam Theorem
• Brouwer Fixed Point Theorem
• Buffon Needle Problem
• Calculus Limerick
• Cantor Diagonalization
• Cantor Set
• Chords of a Unit Circle
• Chords of an Ellipse
• Complex Roots Made Visible
• Computability of Real Numbers
• Conic sections
• Connected Sums
• Continuous but Nowhere Differentiable
• Continuum Hypothesis
• Deal or No Deal
• Dedekind Cuts of Rational Numbers
• Derivative Paradox
• Descartes' Rule of Signs
• Devil's Staircase
• Difference of Squares
• Dinner Party Problem
• Divisibility by Eleven
• Divisibility by Seven
• Does Order of Addition Matter?
• Domino and Square Tilings
• Dominoes on a Chessboard
• Drunken Walker and Fly
• Eccentricity of Conics
• Ellipsoidal Paths
• Envy-free Cake Division
• Equidecomposability
• Euler Characteristic
• Euler's Formula
• Euler's Product Formula
• Face Derivatives and Computer Vision
• Farmers and Pesky Birds
• Fermat's Last Theorem
• Fermat's Little Theorem
• Fibonacci GCD's, please
• Fibonacci Number Formula
• Finding the N-th digit of Pi
• Football Field
• Formula for Primes?
• Four Color Theorem
• Four Fours Problem
• Fourier Ears Only
• Fractional Dimensions
• Fundamental Group
• Gabriel's Trumpet
• Gamma Function
• Gaps in Primes
• Goldbach's Conjecture
• Greedy to Avoid Progressions
• Hailstone Numbers
• Hairy Ball Theorem
• Ham Sandwich Theorem
• High-Dimensional Spheres in Cubes
• Holey Beads
• How GPS Works
• How many Primes?
• How many Rationals?
• Hugging the Equator
• Hyperbolic Geometry
• Impossible Integral?
• Inchworm on a Rubber Rope
• Inductive Tiling
• Irrationality by Infinite Descent
• Isoperimetric Inequality
• Kakeya Needle Problem
• Kaprekar's Constant
• Klein Bottle
• Koch Snowflake
• Koch Tetrahedron
• Large Counterexample
• Largest Known Primes
• Leapfrog Addition
• Liouville Numbers
• Lucas' Theorem
• Magic 1089
• Magic Squares, indeed!
• Making History by Card Shuffling
• Making Magic Squares
• Matching Problem
• Math Limerick
• Medical Tests and Bayes' Theorem
• Memorizing Pi
• Mind-Reading Number Trick
• Misleading Sequence
• Monty Hall Problem
• Morley's Theorem
• Mug Trick
• Multidimensional Newton's Method
• Multiplication by 11
• Multiplication by 111
• Multiplying Complementary Pairs
• Music Math Harmony
• Napoleon's Theorem
• Nine Point Circle
• Odd Numbers in Pascal's Triangle
• One Equals Zero!
• One Equals Zero: Integral Form
• One, Two, Three, Pi
• Ordinal Numbers
• Pascal's Triangle
• Pass the Beer
• Perfect Shuffles
• Pi Approximations
• Pick's Theorem
• Pigeonhole Principle
• Pizza Slices
• Poker Probability Paradox
• Polyhedral Face Vectors
• Powers of Ten in Base Two and Five
• Pretzel Unlinking
• Prime Number Theorem
• Products of Sums of Two Squares
• Projective Planes
• Proof with Words
• Proofs without Words
• Pythagorean Triples
• Quick Square Roots
• Rational Irrational Power
• Rationals Dense but Sparse
• Really Complex Matrices
• Red-Black Card Trick
• Red-Black Pairs Card Trick
• Reflecting on the Hyperbola
• Regular Solids
• Rental Harmony
• Repeating Digits
• Repunit Fun
• Reuleaux Wheel
• Riemann Hypothesis
• Right Double Cone
• Rising Sequences in Card Shuffling
• Rolling Polygons
• Rubber Bands Stuck on a Torus
• Scrabble Identity
• Seven Shuffles
• Shortest Pythagorean Proof?
• Sierpinski-Mazurkiewicz Paradox
• Sine of (1/55555....)
• Six Degrees of Separation
• Slices of Hanging Cubes
• Sliding Chords
• Social Choice and the Condorcet Paradox
• Space-filling Curves
• Sperner's Lemma
• Sphere Eversions
• Spherical Bands
• Spherical Geometry
• Spherical Pythagorean Theorem
• Square Root of Two is Irrational
• Squares Ending in 5
• Squaring Numbers between 40 and 60
• Squaring Quickly
• St. Petersburg Paradox
• Successive Differences of Powers
• Sum of Cubes
• Sum of Cubes and Beyond
• Sum of Prime Reciprocals
• Sums of Reciprocal Powers
• Sums of Three and Four Squares
• Sums of Two Squares
• Sums of Two Squares Ways
• Sure Betting on Different Beliefs
• Surface Area of a Sphere
• Suspended Rope Trick
• Taylor-made Pi
• Tesseract
• Thinned-Out Harmonic Series
• Toggling Light Switches
• Tower of Powers
• Two Envelopes Paradox
• Unbelievable Unlinking
• Van der Waerden Theorem
• Vickrey Auction
• Visual Multiplication with Lines
• Volume of a Ball in N Dimensions
• Volume of a Cone in N Dimensions
• Wallis' Formula
• Whiffle Ball
• Why Does 0.999... = 1?
• Why an International Date Line?
• Wilson's Theorem
• Zero to the Zero Power
• i to the i is a Real Number
• tamreF's Last Theorem