30th

30 (thirty) is the natural number following 29 and preceding 31.

In mathematics

30 is an even, composite, pronic number. With 2, 3, and 5 as its prime factors, it is a regular number and the first sphenic number, the smallest of the form , where is a prime greater than 3. It has an aliquot sum of 42, which is the second sphenic number.

It is also:
* A semiperfect number, since adding some subsets of its divisors (e.g., 5, 10 and 15) equals 30.
* A primorial.
* A Harshad number in decimal.
* Divisible by the number of prime numbers ( 10) below it.
* The largest number such that all coprimes smaller than itself, except for 1, are prime.
* The sum of the first four squares, making it a square pyramidal number.
* The number of vertices in the Tutte–Coxeter graph.
* The measure of the central angle and exterior angle of a dodecagon, which is the petrie polygon of the 24-cell.
* The number of sides of a triacontagon, which in turn is the petrie polygon of the 120-cell and 600-cell.
* The number of sides of a dodecahedron and icosahedron, of vertices of an icosidodecahedron, and of faces of a rhombic dodecahedron.
* The sum of the number of elements of a 5-cell: 5 vertices, 10 edges, 10 faces, and 5 cells.
* The Coxeter number of ''E''₈.

Furthermore,

In a group , such that $, G, =p^\times m$, where does not divide , and has a subgroup of order $p^$, 30 is the only number less than 60 that is neither a prime nor of the aforementioned form. Therefore, 30 is the only candidate for the order of a simple group less than 60, in which one needs other methods to specifically reject to eventually deduce said order.

In science

* The atomic number of zinc is 30.

Astronomy

* Messier object M30, a magnitude 8.5 globular cluster in the constellation Capricornus
* The New General Catalogue object NGC 30, a double star in the constellation Pegasus

Age 30

* The minimum age for United States senators.
* In some regions of the continental United States, the 30th birthday is celebrated by gifting sticks.

In other fields

Thirty is:
* Used (as –30–) to indicate the end of a newspaper (or broadcast) story, a copy editor's typographical notation
* The number of days in the months April, June, September and November (and in unusual circumstances February—see February 30)
* The total number of major and minor keys in Western tonal music, including enharmonic equivalents
* In years of marriage, the pearl wedding anniversary
* The duration in years of the Thirty Years' War - 1618 to 1648
* The code for international direct dial phone calls to Greece
* The house number of 30 St Mary Axe (The Gherkin)
* The number of tracks on The Beatles' eponymous album, usually known as '' The White Album''
* A stage in young adulthood
* Part of the name of:
** 30 Odd Foot of Grunts, the band fronted by actor Russell Crowe
** The movie title ''13 Going on 30'', starring Jennifer Garner
** The title of the Food Network show ''30 Minute Meals''
** ''30 Days of Night'', a comic book miniseries and film
* Judas Iscariot betrayed Jesus for 30 pieces of silver (Matthew 26:15)
* The number of the French department Gard

HOME


Content is Copyleft
Website design, code, and AI is Copyrighted (c) 2014-2017 by Stephen Payne


Consider donating to Wikimedia



As an Amazon Associate I earn from qualifying purchases