Mathematical recreations and puzzles

The Cross Sums is a very common type of logic puzzle that is often referred to as a mathematical transliteration of the crossword. In principle, Cross Sums puzzles are integer programming problems, and can be solved using matrix techniques, although they are typically solved by hand. Cross Sums are regular features in most, if not all, math-and-logic puzzle publications in the United States; Dell Magazines uses the Cross Sums name, which was formerly unique to them but is now in common use among various publishers (although some other names, such as Cross Addition, are still used). In Japan, where the puzzle is called Kakro (カックロ), its popularity is immense, second only to Sudoku among Nikoli's famed logic-puzzle offerings; in an international tapdance, Kappa reprints Nikoli Kakro in the United States, in GAMES Magazine under the name Cross Sums. The Guardian in Britain began printing the puzzle under the name Kakuro in September 2005; since then many other British papers have followed suit and now also print daily puzzles. ...more on Wikipedia about "Cross Sums"

Dots and Boxes (also known as Boxes, Squares, Square-it, Dots and Dashes, or Dots) is a pencil and paper game for two players (or sometimes, more than two). In Mexico dots and boxes is called Timbiriche. ...more on Wikipedia about "Dots and Boxes"

In geometry, flexagons are flat models made from folded strips of paper that can be folded, or flexed, to reveal a number of hidden faces. They are amusing toys but have also caught the interest of mathematicians. ...more on Wikipedia about "Flexagon"

A Friedman number is an integer which, in a given base, is the result of an expression using all its own digits in combination with any of the four basic arithmetic operators (+, -, ×, ÷) and sometimes exponentiation. For example, 347 is a Friedman number since 347 = 73 + 4. The first few base 10 Friedman numbers are ...more on Wikipedia about "Friedman number"

In mathematics, a magic cube is the 3-dimensional equivalent of a magic square, that is, a number of integers arranged in a n x n x n pattern such that the sum of the numbers on each row, each column, each pillar and the four main space diagonals is equal to a single number, the so-called magic constant of the cube, denoted M3(n). It can be shown that if a magic cube consists of the numbers 1, 2, ..., n³, then it has magic constant ...more on Wikipedia about "Magic cube"

The Monty Hall problem is a puzzle in game theory involving probability that is loosely based on the American game show Let's Make a Deal. The name comes from the show's host, Monty Hall. In this puzzle a player is shown three closed doors; behind one is a car, and behind each of the other two is a goat. The player is allowed to open one door, and will win whatever is behind the door. However, after the player selects a door but before opening it, the game host (who knows what's behind the doors) must open another door, revealing a goat. The host then must offer the player an option to switch to the other closed door. Does switching improve the player's chance of winning the car? The answer is yes — switching results in the chances of winning the car improving from 1/3 to 2/3. ...more on Wikipedia about "Monty Hall problem"

The n-puzzle is known in various versions, including the 8 puzzle, the 15 puzzle, and with various names. It is a sliding puzzle that consists of a grid of numbered squares with one square missing, and the labels on the squares jumbled up. If the grid is 3×3, the puzzle is called the 8-puzzle or 9-puzzle. If the grid is 4×4, the puzzle is called the 15-puzzle or 16-puzzle. The goal of the puzzle is to un-jumble the squares by only making moves which slide squares into the empty space, in turn revealing another empty space in the position of the moved piece. ...more on Wikipedia about "N-puzzle"

The Nintendo tumbler puzzle, also known as the Ten Billion Barrel, is a mathematical puzzle in the style of Rubik's Cube. It was invented by Gunpei Yokoi of Nintendo and is covered by U.S. Patent 4,376,537. ...more on Wikipedia about "Nintendo tumbler puzzle"

There are two days held in honor of the mathematical constant π ( Pi): Pi Day and Pi Approximation Day. ...more on Wikipedia about "Pi Day"

Sangaku or San Gaku (算額; lit. mathematical tablet) are Japanese geometrical puzzles in Euclidean geometry on wooden tablets created during the Edo period (1603-1867) by members of all social classes. ...more on Wikipedia about "Sangaku"

Sylver Coinage is a mathematical game for two players, invented by John H. Conway. It is discussed in ...more on Wikipedia about "Sylver coinage"

Tangram ( ) is a Chinese puzzle. While the tangram is often said to be ancient, its existence has only been verified as far back as 1800. ...more on Wikipedia about "Tangram"

The Think-a-Dot was a mathematical toy made by E.S.R. Inc. during the 1960s that demonstrated group theory. It had eight coloured disks on its front, and three holes on its top - left, right, and center - through which a ball bearing could be dropped. Each disk would display either a yellow or blue face, depending on whether the mechanism behind it was tipped to the right or the left. The Think-a-Dot thus had 28=256 internal states. When the ball fell to the bottom it would exit either to a hole on the left or the right of the device. ...more on Wikipedia about "Think-a-Dot"

The Three Cards is a simple but slightly counterintuitive puzzle used as a fairly standard example in probability theory, and a good place to illustrate some basic principles, including the Kolmogorov axioms. ...more on Wikipedia about "Three cards and a top hat"

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The Tower of Hanoi (also called Towers of Hanoi) is a mathematical game or puzzle. It consists of three pegs, and a number of discs of different sizes which can slide onto any peg. The puzzle starts with the discs neatly stacked in order of size on one peg, smallest at the top, thus making a conical shape. ...more on Wikipedia about "Tower of Hanoi"

A vampire number (or true vampire number) is a composite natural number v, with an even number of digits n, that can be factored into two integers x and y each with n/2 digits and not both with trailing zeroes, where v contains all the digits from x and from y, in any order. x and y are called the fangs. ...more on Wikipedia about "Vampire number"

Yellow Pig's Day or Yellow Pig Day ( July 17) is a holiday celebrated by some mathematicians, in recognition of the Yellow Pig and the number 17. ...more on Wikipedia about "Yellow Pig's Day"

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