30 (number)

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

In mathematics

It is a primorial as well as the sum of the squares of the integers 1, 2, 3 and 4. It is the smallest Giuga number.

30 is the smallest sphenic number, and the smallest of the form $2cdot\; 3cdot\; r$ where r is a prime greater than 3. 30 has an aliquot sum of 42; the second sphenic number and all sphenic numbers of this form have an aliquot sum 12 greater than themselves. The aliquot sequence of 30 is 16 members long, it comprises (30,42,54,66,90,144,259,45,33,15,9,4,3,1,0)

Thirty has but one number for which it is the aliquot sum the square number 841. It is the sum of the first four squares, which makes it a square pyramidal number. Adding up some subsets of its divisors (e.g., 5, 10 and 15) gives 30, hence 30 is a semiperfect number.

30 is the largest number such that coprimes smaller than itself are also prime.

A polygon with thirty sides is called a tricontagon. Both an icosahedron and a dodecahedron have 30 edges.

E₈ has Coxeter number 30.

30 is a Harshad number.

In science

• The atomic number of zinc is 30

Astronomy

• Messier object M30, a magnitude 8.5 globular cluster in the constellation Pegasus
• The New General Catalogue object NGC 30, a double star in the constellation Pegasus
• The Saros number of the solar eclipse series which began on October 2, 2069 BC and ended on March 18, 572 BC. The duration of Saros series 30 was 1496.5 years, and it contained 84 solar eclipses. Further, the Saros number of the lunar eclipse series which began on June 19 1803 BC and ended on August 18 487 BC. The duration of Saros series 30 was 1316.2 years, and it contained 74 lunar eclipses.

In other fields

Thirty is:

• Used (as –30–) to indicate the end of a wire story.
• 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 designation of Interstate 30, a freeway that runs from Texas to Arkansas
• The designation of U.S. Route 30, a highway that runs from Oregon to New Jersey
• Various other routes have been numbered "30"; for example, New York State Route 30 which runs from the Pennsylvania border to the Canadian border
• The designation of E30, the European route from Cork to Samara
• 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:
• Thirty 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
• The uniform number of Maury Wills when he played for the Los Angeles Dodgers.
• Judas Iscariot betrayed Jesus for 30 pieces of silver. Matthew 26:15.
• The number of the French department Gard

Historical years

30 A.D., 30 B.C., 1930, 2030, etc.

History and Literature

• At age 30 (according to most biblical scholars) Jesus of Nazareth was baptized by John the Baptist, at the beginning of his public ministry of teaching and healing.
• One of the rallying-cries of the 1960s student/youth protest movement was the slogan, 'Don't trust anyone over thirty'.
• In 'The Myth of Sisyphus' the French existentialist Albert Camus comments that the age of thirty is a crucial period in the life of a man, for at that age he gains a new awareness of the meaning of time.
• In Franz Kafka's novel 'The Trial' Joseph wakes up on the morning of his thirtieth birthday to find himself under arrest for an unspecified crime. After making many futile attempts to find the nature of the crime or the name of his accuser, Joseph dies on the eve of his thirty-first birthday.
• The number of uprights that formed the Sarsen Circle at Stonehenge, also the supposed number of holes forming the arrays of Y and Z Holes at Stonehenge.

Sports

In tennis, the number 30 represents the second point gained in a game.

The California Angels (now Los Angeles Angels) baseball team retired the number in honor of its most notable wearer, Nolan Ryan, on June 16, 1992. (Ryan is the only major league player to have his number retired by three different teams, though the other two teams retired number 34 for him rather than 30). The San Francisco Giants extended the same honor to Orlando Cepeda. Nick Swisher of the Chicago White Sox wears the number 30 and is known as "The Dirty 30".

Music

• 30, album from 2001 by Harry Connick, Jr.
• 30 Seconds to Mars
• 30 Minutes, a song by t.A.T.u

Movies

• 30 Days of Night

References

• Prime Curios! 30 from the Prime Pages