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perfect number

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perfect number

 
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–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; ME
Dictionary.com Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2009.
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perfect number  
n.  A positive integer that is equal to the sum of its positive integral factors, including 1 but excluding itself.
The American Heritage® Dictionary of the English Language, Fourth Edition
Copyright © 2009 by Houghton Mifflin Company.
Published by Houghton Mifflin Company. All rights reserved.
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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
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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Encyclopedia

perfect number

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. It is known, however, that the Pythagoreans (founded c. 525 BC) studied perfect numbers for their "mystical" properties.

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Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.
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