28
Cardinal	twenty-eight
Ordinal	twenty-eighth
Factorization
Roman numeral	XXVIII
Binary	11100
Hexadecimal	1C

Mathematics

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.

Other fields

• 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).
• The year AD 28.