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2. Multiply perfect number - Wikipedia

   en.wikipedia.org/wiki/Multiply_perfect_number

   In mathematics, a multiply perfect number (also called multiperfect number or pluperfect number) is a generalization of a perfect number. For a given natural number k , a number n is called k -perfect (or k -fold perfect) if the sum of all positive divisors of n (the divisor function , σ ( n )) is equal to kn ; a number is thus perfect if and ...

3. 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 ...

4. 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.

5. Table of divisors - Wikipedia

   en.wikipedia.org/wiki/Table_of_divisors

   a perfect number equals the sum of its proper divisors; that is, s(n) = n; an abundant number is lesser than the sum of its proper divisors; that is, s(n) > n; a highly abundant number has a sum of positive divisors that is greater than any lesser number; that is, σ(n) > σ(m) for every positive integer m < n.

6. 28 (number) - Wikipedia

   en.wikipedia.org/wiki/28_(number)

   The number 28 depicted as 28 balls arranged in a triangular pattern with the number of layers of 7 28 as the sum of four nonzero squares. Twenty-eight is a composite number and the second perfect number as it is the sum of its proper divisors: 1 + 2 + 4 + 7 + 14 = 28 {\displaystyle 1+2+4+7+14=28} .

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