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.

perfect number

noun

1. an integer, such as 28, that is equal to the sum of all its possible factors, excluding itself

perfect number

1. 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.

Word History and Origins

Origin of perfect number¹

Middle English word dating back to 1350–1400

Example Sentences

Six is a perfect number, and seven is a prime number, but only a glutton for punishment would put them together in front of a bunch of 13-year-olds.

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“They’re a novelty. They’re really hard to build and they’re not as rewarding as a really good 18-hole course. I don’t know how many reversible courses are in existence right now but, in my opinion, it’s the perfect number.”

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It was a shift in mood as Maresca said earlier in April that the frontman was his "perfect number nine" and wanted "a copy of Nico" rather than to replace him.

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Still, the president insists that “Inflation is now down to the perfect number. We’ve ended Biden’s inflation nightmare…There’s hardly any inflation at all.”

Read more on Salon

Soil experts differ on the perfect number between acidity and alkalinity, but the sweet spot is generally believed to be between 6.5 and 7.2, Wallace said, and some scientists believe plants in SoCal can tolerate alkalinity as high as 7.9.

Read more on Los Angeles Times