Perfect number (English Wikipedia)

Analysis of information sources in references of the Wikipedia article "Perfect number" in English language version.

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oeis.org (Global: 742nd place; English: 538th place)

  • All factors of are congruent to 1 mod 2p. For example, 211 − 1 = 2047 = 23 × 89, and both 23 and 89 yield a remainder of 1 when divided by 22. Furthermore, whenever p is a Sophie Germain prime—that is, 2p + 1 is also prime—and 2p + 1 is congruent to 1 or 7 mod 8, then 2p + 1 will be a factor of which is the case for p = 11, 23, 83, 131, 179, 191, 239, 251, ... OEISA002515.
  • "A000396 - OEIS". oeis.org. Retrieved 2024-03-21.

quantamagazine.org (Global: 6,413th place; English: 4,268th place)

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  • Weisstein, Eric W. "Perfect Number". mathworld.wolfram.com. Retrieved 2025-02-09. Perfect numbers are positive integers n such that n=s(n), where s(n) is the restricted divisor function (i.e., the sum of proper divisors of n), ...
  • Weisstein, Eric W. "Perfect Number". MathWorld.

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zbmath.org (Global: 1,923rd place; English: 1,068th place)