Twenty-eight

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

• The atomic number of nickel.
• The number of days in the shortest month of the Gregorian calendar, February. (Except on leap years, when there are twenty-nine.)
• The common name for the parrot Barnardius zonarius semitorquatus, widely distributed in Western Australia and South Australia. Its call sounds like "wenniate".
• The number of letters in the Danish and Swedish alphabets.
• In neo-Nazi circles, twenty-eight indicates Blood and Honour (28 = BH - B - second letter of the alphabet and H - the eight letter).

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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.