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  2. MacMahon Squares - Wikipedia

    en.wikipedia.org/wiki/MacMahon_Squares

    The goal is to arrange the squares into a 4 by 6 grid so that when two squares share an edge, the common edge is the same color in both squares. In 1964, a supercomputer was used to produce 12,261 solutions to the basic version of the MacMahon Squares puzzle, with a runtime of about 40 hours. [2]

  3. Four color theorem - Wikipedia

    en.wikipedia.org/wiki/Four_color_theorem

    [3] The theorem is a stronger version of the five color theorem, which can be shown using a significantly simpler argument. Although the weaker five color theorem was proven already in the 1800s, the four color theorem resisted until 1976 when it was proven by Kenneth Appel and Wolfgang Haken. This came after many false proofs and mistaken ...

  4. Boolean Pythagorean triples problem - Wikipedia

    en.wikipedia.org/wiki/Boolean_Pythagorean...

    The problem asks if it is possible to color each of the positive integers either red or blue, so that no Pythagorean triple of integers a, b, c, satisfying + = are all the same color. For example, in the Pythagorean triple 3, 4, and 5 ( 3 2 + 4 2 = 5 2 {\displaystyle 3^{2}+4^{2}=5^{2}} ), if 3 and 4 are colored red, then 5 must be colored blue.

  5. Casus irreducibilis - Wikipedia

    en.wikipedia.org/wiki/Casus_irreducibilis

    Casus irreducibilis (from Latin 'the irreducible case') is the name given by mathematicians of the 16th century to cubic equations that cannot be solved in terms of real radicals, that is to those equations such that the computation of the solutions cannot be reduced to the computation of square and cube roots.

  6. Eight queens puzzle - Wikipedia

    en.wikipedia.org/wiki/Eight_queens_puzzle

    In the case of knights, an easy solution is to place one on each square of a given color, since they move only to the opposite color. The solution is also easy for rooks and kings. Sixteen kings can be placed on the board by dividing it into 2-by-2 squares and placing the kings at equivalent points on each square.

  7. Mutilated chessboard problem - Wikipedia

    en.wikipedia.org/wiki/Mutilated_chessboard_problem

    A domino placed on the chessboard will always cover one white square and one black square. Therefore, any collection of dominoes placed on the board will cover equal numbers of squares of each color. But any two opposite squares have the same color: both black or both white. If they are removed, there will be fewer squares of that color and ...

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  9. Hilbert's seventeenth problem - Wikipedia

    en.wikipedia.org/wiki/Hilbert's_seventeenth_problem

    which cannot be represented as a sum of squares of other polynomials. In 1888, Hilbert showed that every non-negative homogeneous polynomial in n variables and degree 2d can be represented as sum of squares of other polynomials if and only if either (a) n = 2 or (b) 2d = 2 or (c) n = 3 and 2d = 4. [2]