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Twenty-eight (28) is the natural number following twenty-seven and preceding twenty-nine. It is is a composite number, its proper divisors being 1, 2 and 7, and its factorization is

Twenty-eight is the sum of the first five prime numbers, as well as a triangular number and the second perfect number. The next perfect number is 496.

Twenty-eight is also

See also: twenty-six, twenty-seven, twenty-nine, thirty, integer, list of numbers.

This article is about the number. For the year AD 28, see 28.