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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. 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. Friendly number - Wikipedia

   en.wikipedia.org/wiki/Friendly_number

   The smallest friendly number is 6, forming for example, the friendly pair 6 and 28 with abundancy σ(6) / 6 = (1+2+3+6) / 6 = 2, the same as σ(28) / 28 = (1+2+4+7+14+28) / 28 = 2. The shared value 2 is an integer in this case but not in many other cases. Numbers with abundancy 2 are also known as perfect numbers. There are several unsolved ...

6. Field (mathematics) - Wikipedia

   en.wikipedia.org/wiki/Field_(mathematics)

   Informally, a field is a set, along with two operations defined on that set: an addition operation written as a + b, and a multiplication operation written as a ⋅ b, both of which behave similarly as they behave for rational numbers and real numbers, including the existence of an additive inverse −a for all elements a, and of a multiplicative inverse b −1 for every nonzero element b.

7. Multiplicative number theory - Wikipedia

   en.wikipedia.org/wiki/Multiplicative_number_theory

   A large part of analytic number theory deals with multiplicative problems, and so most of its texts contain sections on multiplicative number theory. These are some well-known texts that deal specifically with multiplicative problems: Davenport, Harold (2000). Multiplicative Number Theory (3rd ed.). Berlin: Springer. ISBN 978-0-387-95097-6.

8. 29 (number) - Wikipedia

   en.wikipedia.org/wiki/29_(number)

   29 is the fifth primorial prime, like its twin prime 31.. 29 is the smallest positive whole number that cannot be made from the numbers {,,,}, using each digit exactly once and using only addition, subtraction, multiplication, and division. [1]

9. List of numbers - Wikipedia, the free encyclopedia

   en.wikipedia.org/wiki/List_of_numbers

   A list of articles about numbers (not about numerals). Topics include powers of ten, notable integers, prime and cardinal numbers, and the myriad system.