# 30 (number): Map

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

## In mathematics

30 is the sum of the first four squares, which makes it a square pyramidal number.

It is a primorial and is the smallest Giuga number.

30 is the smallest sphenic number, and the smallest of the form 2\cdot 3\cdot 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.

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.

Since any group G such that |G| = pnm, where p does not divide m, has a subgroup of order pn, and 30 is the only number less than 60 that is not either a prime or of the above form, it is the only candidate for the order of a simple group less than 60 that one needs other methods to reject.

Thirty is:

## 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.
• Western Christianity's most prolific 20th century essayist, F. W. Boreham in 'Life at Thirty' ('Cliffs of Opal') mentions that in addition to Jesus commencing ministry at 30 (Luke 3:23), Joseph was 30 when he stood before Pharaoh, King of Egypt (Genesis 41:46), King David was 30 when he began to reign (2 Samuel 5:4), and the Levites were numbered from the age of 30 and upward (1 Chronicles 23:3). Also in that essay Boreham writes 'It was said of [the English poet] Keats, that "he ensphered himself in thirty perfect years and died, not young".'

## 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".
• 30 is one of the more common numbers worn by hockey goaltenders (along with 31).
• The number of New Jersey Devils goalie, Martin Brodeur

## References

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