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  2. Square number - Wikipedia

    en.wikipedia.org/wiki/Square_number

    In mathematics, a square number or perfect square is an integer that is the square of an integer; [1] ... 15 2 = 225 16 2 = 256 17 2 = 289 18 2 = 324 19 2 = 361. 20 2 ...

  3. Perfect number - Wikipedia

    en.wikipedia.org/wiki/Perfect_number

    In number theory, a perfect number is a positive integer that is equal to the sum of its positive proper divisors, that is, divisors excluding the number itself. For instance, 6 has proper divisors 1, 2 and 3, and 1 + 2 + 3 = 6, so 6 is a perfect number. The next perfect number is 28, since 1 + 2 + 4 + 7 + 14 = 28.

  4. List of Mersenne primes and perfect numbers - Wikipedia

    en.wikipedia.org/wiki/List_of_Mersenne_primes...

    So, 6 is a perfect number because the proper divisors of 6 are 1, 2, and 3, and 1 + 2 + 3 = 6. [2] [4] There is a one-to-one correspondence between the Mersenne primes and the even perfect numbers, but it is unknown whether there exist odd perfect numbers. This is due to the Euclid–Euler theorem, partially proved by Euclid and completed by ...

  5. 15 (number) - Wikipedia

    en.wikipedia.org/wiki/15_(number)

    M = 15 The 15 perfect matchings of K 6 15 as the difference of two positive squares (in orange).. 15 is: The eighth composite number and the sixth semiprime and the first odd and fourth discrete semiprime; [1] its proper divisors are 1, 3, and 5, so the first of the form (3.q), [2] where q is a higher prime.

  6. List of types of numbers - Wikipedia

    en.wikipedia.org/wiki/List_of_types_of_numbers

    Such a number is algebraic and can be expressed as the sum of a rational number and the square root of a rational number. Constructible number: A number representing a length that can be constructed using a compass and straightedge. Constructible numbers form a subfield of the field of algebraic numbers, and include the quadratic surds.

  7. Superperfect number - Wikipedia

    en.wikipedia.org/wiki/Superperfect_number

    An odd superperfect number n would have to be a square number such that either n or ... perfect numbers are (1,2)-perfect, ... 15, 1023, 29127, 355744082763

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  9. Triangular number - Wikipedia

    en.wikipedia.org/wiki/Triangular_number

    A square whose side length is a triangular number can be partitioned into squares and half-squares whose areas add to cubes. This shows that the square of the n th triangular number is equal to the sum of the first n cube numbers. Also, the square of the n th triangular number is the same as the sum of the cubes of the integers 1 to n.