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perfect number
Sign in to savepositive integer which equals the sum of all its divisors
A perfect number is a positive integer that equals the sum of all its divisors (the numbers that divide evenly into it). Mathematicians find perfect numbers interesting because they are rare and have unique mathematical properties, making them a subject of study in number theory.
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Encyclopedic overview
Illustration of the perfect number status of the number 6
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, because 28 has proper divisors 1, 2, 4 , 7, 14, and 1 + 2 + 4 + 7 + 14 = 28.
Excerpted from Wikipedia’s “perfect number” article, available under the CC BY-SA 4.0 licence.
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