# perfect number

noun, Mathematics
1.
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 of perfect number
1350-1400
1350-1400; Middle English
Dictionary.com Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2015.
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Examples from the Web for perfect number
Historical Examples
• “There are never more than seven crackers on a plate—just seven, the perfect number,” sighed this hyperbolical girl.

Annie Roe Carr
• Canaan is a type of holiness, and seven is the perfect number.

W. E. Shepard
• Therefore, too, Aristotle thought there were five elements, since the uneven and perfect number had everywhere the predominance.

Plutarch
• Thousand is a perfect number, and no number extends beyond it.

• But here again he was uncertain whether the ‘perfect number’ was ten or six.

Various
• Ten was a perfect number, and is that of the commandments given to Moses.

• Seven was a perfect number, and therefore the victims should be seven.

W. G. Blaikie
• And in reply, another remarked, 'Seven is the perfect number, and seven times seven is perfection.'

Harriet Beecher Stowe
• Six was a perfect number—that is, equal to the sum of all its factors—an additional reason why there must be exactly six planets.

• A perfect number (Greek), as already stated, is one which is equal to the sum of its divisors.

Plato
British Dictionary definitions for perfect number

## perfect number

noun
1.
an integer, such as 28, that is equal to the sum of all its possible factors, excluding itself
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
© William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
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perfect number in Science
 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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### Difficulty index for perfect number

Few English speakers likely know this word

### Word Value for perfect

14
16
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