28 (number) - Wikipedia
https://en.wikipedia.org/wiki/28_(number)
It is a composite number; a square-prime, of the form (p ,q) where q is a higher prime. It is the third of this form and of the specific form (2 .q), with proper divisors being 1, 2, 4, 7, and 14. Twenty-eight is the second perfect number - it is the sum of its proper divisors: $${\displaystyle 1+2+4+7+14=28}$$. As a perfect number, it is related to the Mersenne prime 7, sin… See more
DA: 91 PA: 83 MOZ Rank: 2