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

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

“There is no perfect number to send, no perfect geography to send it out to,” Galperin said.

From Los Angeles Times ● Jan. 24, 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

Matsuyama switched to a 3-wood off the tee and had 276 yards to the flag, a perfect number for a high, cut 3-wood.

From Seattle Times ● Jan. 16, 2022

Let me see; that's seven times we've stayed home from the Holy Land, isn't it?—the perfect number.

From The End of the Rainbow by MacGregor, Mary Esther Miller