Perfect number - Wikipedia, the free encyclopedia
In mathematics, a perfect number is defined as a positive integer which is the sum of its proper positive divisors, that is, the sum of the positive divisors excluding the number itself. Equivalentl...
en.wikipedia.org/wiki/Perfect_number
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28 (number) - Wikipedia, the free encyclopedia
28 ( twenty-eight ) is the natural number following 27 and preceding 29. It is a composite number, its proper divisors being 1, 2, 4, 7, and 14. Twenty-eight is classed as a perfect number because ...
en.wikipedia.org/wiki/28_(number)
It is known that all even perfect numbers (except 6) end in 16, 28, 36, 56, 76, or 96 (Lucas 1891) and have digital root 1. In particular, the last digits ...
mathworld.wolfram.com/PerfectNumber.html mathworld.wolfram.com/PerfectNumber.html
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Yes it is. 6 is the first perfect number, 28 is the second perfect number.
http://wiki.answers.com/Q/Is_28_a_perfect_number
The History of The Earth; Before History; Prehistoric; ... Precambrian Time began about 4.5 billion years ago. ... Stand with your arms held out to each side and let the extent of the earth's history be represented by the distance from the tips of your fingers on your left hand to the tips of the fingers on your right.
www.boscobel.k12.wi.us/~schnrich/the_geologic_time_scal... www.boscobel.k12.wi.us/~schnrich/the_geologic_time_scale.htm
From Ivars Peterson's MathTrek column in MAA Online. Curious relationships satisfied by perfect numbers. ... In the course of preparing a unit on number theory for one of his classes, he noticed a striking pattern involving the perfect number 28: He tried the next perfect number:
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Six ( 6 ) is the first perfect number, because 1, 2 and 3 are its proper positive divisors and 1 + 2 + 3 = 6. The next perfect number is 28 = 1 + 2 + 4 + 7 + 14. The next perfect numbers are 496 and 8128 . These first four perfect numbers were the only ones known to the Ancient Greeks .
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Britannica online encyclopedia article on perfect number (mathematics), a positive integer that is equal to the sum of its proper divisors. The smallest perfect number is 6, which is the sum of 1, 2, and 3. Other perfect numbers are 28, 496, and 8,128. The discovery of such numbers is lost in prehistory. ... number game...
www.britannica.com/EBchecked/topic/451491/perfect-numbe... www.britannica.com/EBchecked/topic/451491/perfect-number
types of numbers - Different kinds of Numbers Perfect number -number whose divisors (except itself) add up to itself. For example,. 28 is a perfect number. Its proper divisors are {1, 2, 4, 7, 14} and 1 +2 +4 +7 +14 ... Perfect number -number whose divisors (except itself) add up to itself. For example,. 28 is a perfect number.
piyushdadriwala.sulekha.com/blog/post/2007/11/types-of-... piyushdadriwala.sulekha.com/blog/post/2007/11/types-of-numbers.htm
As a perfect number, it is related to the Mersenne prime 7, since 22(23 - 1) = 28. The next perfect number is 496. Twenty-eight is a triangular number, a hexagonal number and a centered nonagonal number. Twenty-eight is the sum of the first five prime numbers.
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