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  2. Ulam spiral - Wikipedia

    en.wikipedia.org/wiki/Ulam_spiral

    [7] [8] Klauber describes his construction as follows, "The integers are arranged in triangular order with 1 at the apex, the second line containing numbers 2 to 4, the third 5 to 9, and so forth. When the primes have been indicated, it is found that there are concentrations in certain vertical and diagonal lines, and amongst these the so ...

  3. List of prime numbers - Wikipedia

    en.wikipedia.org/wiki/List_of_prime_numbers

    A prime number (or prime) is a natural number greater than 1 that has no positive divisors other than 1 and itself. By Euclid's theorem, there are an infinite number of prime numbers. Subsets of the prime numbers may be generated with various formulas for primes.

  4. 200 (number) - Wikipedia

    en.wikipedia.org/wiki/200_(number)

    The number appears in the Padovan sequence, preceded by 86, 114, 151 (it is the sum of the first two of these). [1] The sum of Euler's totient function φ(x) over the first twenty-five integers is 200. 200 is the smallest base 10 unprimeable number – it cannot be turned into a prime number by changing just one of its digits to any other digit.

  5. Mathematics of Sudoku - Wikipedia

    en.wikipedia.org/wiki/Mathematics_of_Sudoku

    A Sudoku with 24 clues, dihedral symmetry (a 90° rotational symmetry, which also includes a symmetry on both orthogonal axis, 180° rotational symmetry, and diagonal symmetry) is known to exist, but it is not known if this number of clues is minimal for this class of Sudoku. [5]

  6. Grid method multiplication - Wikipedia

    en.wikipedia.org/wiki/Grid_method_multiplication

    The grid method (also known as the box method) of multiplication is an introductory approach to multi-digit multiplication calculations that involve numbers larger than ten. Because it is often taught in mathematics education at the level of primary school or elementary school , this algorithm is sometimes called the grammar school method.

  7. Table of prime factors - Wikipedia

    en.wikipedia.org/wiki/Table_of_prime_factors

    An economical number has been defined as a frugal number, but also as a number that is either frugal or equidigital. gcd( m , n ) ( greatest common divisor of m and n ) is the product of all prime factors which are both in m and n (with the smallest multiplicity for m and n ).

  8. Nonogram - Wikipedia

    en.wikipedia.org/wiki/Nonogram

    A completed nonogram of the letter "W" from the Wikipedia logo. Nonograms, also known as Hanjie, Paint by Numbers, Picross, Griddlers, and Pic-a-Pix, are picture logic puzzles in which cells in a grid must be colored or left blank according to numbers at the edges of the grid to reveal a hidden picture.

  9. Abundant number - Wikipedia

    en.wikipedia.org/wiki/Abundant_number

    Marc Deléglise showed in 1998 that the natural density of the set of abundant numbers and perfect numbers is between 0.2474 and 0.2480. [4] An abundant number which is not the multiple of an abundant number or perfect number (i.e. all its proper divisors are deficient) is called a primitive abundant number