perfect-number

perfect number

noun Mathematics.
a positive number that is equal to the sum of all positive integers that are submultiples of it, as 6, which is equal to the sum of 1, 2, and 3.


Origin:
1350–1400; Middle English

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Collins
World English Dictionary
perfect number
 
n
an integer, such as 28, that is equal to the sum of all its possible factors, excluding itself

Collins English Dictionary - Complete & Unabridged 10th Edition
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American Heritage
Science Dictionary
perfect number  
A positive integer that equals the sum of all of its divisors other than itself. An example is 28, whose divisors (not counting itself) are 1, 2, 4, 7, and 14, which added together give 28.
The American Heritage® Science Dictionary
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