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

See Examples For:

perfect number

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

"Without the scientific study, it can’t be said what will be the perfect number for Mount Everest," he said.

From BBC ● Jun. 6, 2024

“We haven’t settled on what the perfect number is. Maybe we never will, but I can’t imagine it being less than 18.”

From Seattle Times ● Feb. 22, 2023

Seven was, among the Hebrews, their perfect number; and hence we see it continually recurring in all their sacred rites.

From The Symbolism of Freemasonry by Mackey, Albert G.