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  2. Multiply perfect number - Wikipedia

    en.wikipedia.org/wiki/Multiply_perfect_number

    It can be proven that: . For a given prime number p, if n is p-perfect and p does not divide n, then pn is (p + 1)-perfect.This implies that an integer n is a 3-perfect number divisible by 2 but not by 4, if and only if n/2 is an odd perfect number, of which none are known.

  3. List of Mersenne primes and perfect numbers - Wikipedia

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

    For example, 3 is a Mersenne prime as it is a prime number and is expressible as 2 2 − 1. [ 1 ] [ 2 ] The exponents p corresponding to Mersenne primes must themselves be prime, although the vast majority of primes p do not lead to Mersenne primes—for example, 2 11 − 1 = 2047 = 23 × 89 .

  4. Perfect number - Wikipedia

    en.wikipedia.org/wiki/Perfect_number

    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. The first four perfect numbers are 6, 28, 496 and 8128. [2] The sum of proper divisors of a number is called its aliquot sum, so a perfect number is one that is equal to its aliquot sum.

  5. 10, 9, 8, 7, 6, 5, 4, 3, 2, 1 - Wikipedia

    en.wikipedia.org/wiki/10,_9,_8,_7,_6,_5,_4,_3,_2,_1

    10, 9, 8, 7, 6, 5, 4, 3, 2, 1 is the fourth studio album by Midnight Oil, released in 1982 by Columbia Records. It hit number 3 on the Australian Kent Music Report Albums Chart during 171 total weeks. [1] The band's first US release, it peaked at number 178 on the Billboard 200. At the Countdown Music Awards, it was nominated for Best ...

  6. Collatz conjecture - Wikipedia

    en.wikipedia.org/wiki/Collatz_conjecture

    Equivalently, ⁠ 2n − 1 / 3 ⁠ ≡ 1 (mod 2) if and only if n ≡ 2 (mod 3). Conjecturally, this inverse relation forms a tree except for a 1–2 loop (the inverse of the 1–2 loop of the function f(n) revised as indicated above).

  7. PSL (2,7) - Wikipedia

    en.wikipedia.org/wiki/PSL(2,7)

    In fact, PSL(2, 7) is the second smallest nonabelian simple group, after the alternating group A 5 = PSL(2, 5) = PSL(2, 4). The number of conjugacy classes and irreducible representations is 6. The sizes of conjugacy classes are 1, 21, 42, 56, 24, 24. The dimensions of irreducible representations 1, 3, 3, 6, 7, 8. Character table

  8. 1 + 2 + 3 + 4 + ⋯ - Wikipedia

    en.wikipedia.org/wiki/1_%2B_2_%2B_3_%2B_4_%2B_%E...

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  9. Pell number - Wikipedia

    en.wikipedia.org/wiki/Pell_number

    This sequence of approximations begins ⁠ 1 / 1 ⁠, ⁠ 3 / 2 ⁠, ⁠ 7 / 5 ⁠, ⁠ 17 / 12 ⁠, and ⁠ 41 / 29 ⁠, so the sequence of Pell numbers begins with 1, 2, 5, 12, and 29. The numerators of the same sequence of approximations are half the companion Pell numbers or Pell–Lucas numbers ; these numbers form a second infinite ...