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.

---

perfect number British  

noun

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

---

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.

---

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

"In light of the weekend's events, I don't think it could have been a more perfect number."

From Reuters ● Mar. 14, 2023

Something, perhaps, there is in its being a perfect number, formed of seven multiplied by four, and withal the first number, after six, that is equal to all its parts.

From Ideal Commonwealths by Sir Saint Thomas More