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  2. Associative magic square - Wikipedia

    en.wikipedia.org/wiki/Associative_magic_square

    The number zero for n = 6 is an example of a more general phenomenon: associative magic squares do not exist for values of n that are singly even (equal to 2 modulo 4). [3] Every associative magic square of even order forms a singular matrix, but associative magic squares of odd order can be singular or nonsingular. [4]

  3. 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.

  4. 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 ...

  5. Magic constant - Wikipedia

    en.wikipedia.org/wiki/Magic_constant

    The normal magic constant of order n is ⁠ n 3 + n / 2 ⁠. The largest magic constant of normal magic square which is also a: triangular number is 15 (solve the Diophantine equation x 2 = y 3 + 16y + 16, where y is divisible by 4); square number is 1 (solve the Diophantine equation x 2 = y 3 + 4y, where y is even);

  6. Magic square - Wikipedia

    en.wikipedia.org/wiki/Magic_square

    Odd squares: For the 3×3 odd square, since α, β, and γ are in arithmetic progression, their sum is equal to the product of the square's order and the middle term, i.e. α + β + γ = 3 β. Thus, the diagonal sums will be equal if we have β s in the main diagonal and α , β , γ in the skew diagonal.

  7. Pandiagonal magic square - Wikipedia

    en.wikipedia.org/wiki/Pandiagonal_magic_square

    All 4 × 4 pandiagonal magic squares using numbers 1-16 without duplicates are obtained by letting a equal 1; letting b, c, d, and e equal 1, 2, 4, and 8 in some order; and applying some translation. For example, with b = 1 , c = 2 , d = 4 , and e = 8 , we have the magic square

  8. 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 ...

  9. Van der Waerden's theorem - Wikipedia

    en.wikipedia.org/wiki/Van_der_Waerden's_theorem

    Van der Waerden's theorem is a theorem in the branch of mathematics called Ramsey theory.Van der Waerden's theorem states that for any given positive integers r and k, there is some number N such that if the integers {1, 2, ..., N} are colored, each with one of r different colors, then there are at least k integers in arithmetic progression whose elements are of the same color.