perfect number

American  

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.

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perfect number British  

noun

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

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perfect number Scientific  

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.

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Etymology

Origin of perfect number

Middle English word dating back to 1350–1400

Example Sentences

I always felt like three seasons was sort of a perfect number for a smaller show like this.

From Los Angeles Times • Feb. 17, 2026

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.

From The Wall Street Journal • Oct. 14, 2025

For me Bob Latchford was the perfect number nine, his buccaneering style was suited to that era in the '70s and early '80s.

From BBC • Apr. 13, 2023

The 32-team lineup is the perfect number for a knockout bracket.

From Seattle Times • Mar. 29, 2022

One is the perfect number; it is the primitive monad.

From The Heroic Enthusiasts (Gli Eroici Furori) Part the First An Ethical Poem by Williams, L.