28 (number)

From Academic Kids

28 (twenty-eight) is the natural number following 27 and preceding 29.

<< 20 21 22 23 24 25 26 27 28 29 >> List of numbers -- Integers Template:Numbers (0 E2)
Cardinal	twenty-eight
Ordinal	twenty-eighth
Factorization	<math>2^2 \cdot 7<math>
Roman numeral	XXVIII
Binary	11100
Hexadecimal	1C

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In mathematics

It is a composite number, its proper divisors being 1, 2, 4, 7 and 14, making it a perfect number and a harmonic divisor number.

Twenty-eight is the second perfect number. As a perfect number, it is related to the Mersenne prime 7, since 2²(2³ - 1) = 28. The next perfect number is 496.

Twenty-eight is a triangular number, a hexagonal number and a centered nonagonal number. Twenty-eight is the sum of the first five prime numbers.

It is also a Keith number, because it recurs in a Fibonacci-like sequence started from its base 10 digits: 2, 8, 10, 18, 28...

Twenty-eight is the ninth and last number in early Indian Magic square of order 3.

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In science

The atomic number of nickel
The fourth Magic number (physics)

In astronomy,

Messier object M28, a magnitude 8.5 globular cluster in the constellation Sagittarius

The New General Catalogue object (http://www.ngcic.org/) NGC 28, an elliptical galaxy in the constellation Phoenix

The Saros number (http://sunearth.gsfc.nasa.gov/eclipse/SEsaros/SEsaros1-175.html) of the solar eclipse series which began on -1910 March 22 and ended on -630 April 28. The duration of Saros series 28 was 1280.1 years, and it contained 72 solar eclipses.

The Saros number (http://sunearth.gsfc.nasa.gov/eclipse/LEsaros/LEsaros1-175.html) of the lunar eclipse series which began on -1915 June 27 and ended on -581 September 6. The duration of Saros series 28 was 1334.2 years, and it contained 75 lunar eclipses.

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In other fields

Twenty-eight is:

The number of days in the shortest month of the Gregorian calendar, February. (Except in 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 (not counting W), amd also in the Arabic and Esperanto alphabets.
In neo-Nazi circles, twenty-eight indicates Blood and Honour (28 = BH - B - second letter of the alphabet and H - the eight letter).
Part of the title of a romantic comedy movie 28 Days, and an unrelated science fiction movie 28 Days Later.
Part of the name of a well known indie rock band from Melbourne, Australia called 28 Days - the name is unrelated to either of the movies above.
Historical years: 28 A.D., 28 B.C., or 1928
The number of Chinese constellations, "Xiu" or "mansions" (a literal translation), equivalent to the 12 western zodiac constellations.
The number of normal human teeth, not including the third molars (wisdom teeth).
The number of dominoes in standard domino sets.
The number of Scudetto won by Turin-based football club, Juventus.