It is a Composite Number , its proper Divisor s 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 , the previous being 6 .
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 appears in the Padovan Sequence , preceded by the terms 12, 16, 21 (it is the sum of the first two of these).
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.
- The 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 Planet Saturn revolves around the Sun in approximately 28 Years . This is acknowledged in Astrology and in cultures or religions that base partly on it (see below, other fields)
is:
- The number of days in the shortest Month of the Gregorian Calendar , February (except in Leap Year s, when there are twenty-nine). All twelve months of the Gregorian calendar have at least 28 days, regardless of the year.
- Years normally follow a 28-year cycle, since there are seven days in a week and leap year occurs every four years; a calendar from 28 years ago is the same as this year's (a year like 1900, non-leap though divisible by four, breaks the pattern).
- 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 Alphabet s (not counting W), and also in the Arabic and Esperanto Alphabet s.
- 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 B.C. , or 1928
- The number of Chinese Constellation s, "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 .
- Deriving from the 28 year cycle of Saturn s revolution around the Sun , the 28-year cycle as well as its subdivisions by 14 and 7 are supposed in Astrology to mark significant turning points or sections in the course of a persons development in life. Thus, the number 28 has special significance in the culture of religious sects such as the Kadiri and the Mevlevi dervishes. The 28-beat metric pattern often used in the music compositions accompanying the main part of the Mevlevi Sema ritual is called the "Devri kebir", meaning the "Big Circle" and is a reference to above astronomical facts about the year and the Saturn year.
- In Québec , Fran%C3%A7ois P%C3%A9russe , in one of his best-selling Album Du Peuple made a parody of Wheel Of Fortune in which all of the letters picked by the contestant were present 28 times. As a result, 28 became an almost Mythical Number used by many Québec youths, the phrase "Y'en a 28" (There are 28 {Link without Title} ) became a Running Gag still used and recognized more than 15 years later.
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