The 13 (number) reference article from the English Wikipedia on 24-Apr-2004 (provided by Fixed Reference: snapshots of Wikipedia from wikipedia.org)

13 (number)

13 (Thirteen) is the natural number following 12 and preceding 14.

List of numbers — Integers
0 8 9 10 11 12 13 14 15 16 17 18 20
Cardinal	thirteen
Ordinal	thirteenth
Numeral system
Factorization	prime number>prime
Roman numeral	XIII
Binary	1101
Hexadecimal	D

In mathematics

Thirteen is the 6th smallest prime number, the next is seventeen.

It is the seventh Fibonacci number.

13 goes into 999,999 exactly 76,923 times, so fractions with 13 in the denominator have six digit repeating sequences in their decimal expansions.

At 13, the Mertens function sets a new low of -3, subseded later at 31 with a value of -4.

As lucky, unlucky, or significant number

Regarded as an unlucky number in many cultures. Unreasoned fear of the number 13 is termed triskaidekaphobia. Due to this fear, some tall buildings have resorted to skipping the "thirteenth floor", simply by numbering it "14" (though it's really still the thirteenth floor) or having a 12a-th floor instead. The thirteenth of a month is likewise ominous, at least when it falls on a Friday (see Friday the 13th). The 13th falls on a Friday more often than any other day. In fact it occurs more often than any other day/number combination except those that coincide with it (Thursday the 12th, Saturday the 14th, etc).

In the Christian religion, the number is considered significant since there were thirteen present at the Last Supper. Also, if both Judas and Matthias are counted, there were thirteen apostles. Thirteen was also once associated with the Epiphany by Christians, the Christ child having received the Magi on his thirteenth day of life.

Regarded as a lucky number in China because it is synonymous with '實生'; which means "must be alive". However 13 is regarded as unlucky by those Chinese under the influence of foreign cultures.

In other fields

Thirteen is:

• The atomic number of aluminum.
• The ASCII and Unicode value for carriage return.
• The number of loaves in a baker's dozen.
• 'Unlucky for some', according to bingo callers.
• The number of Archimedean solids.
• The number of dimensions in some theories of relativity.
• The number of players in a rugby league team.
• The age of maturity in Jewish tradition. Boys get their bar mitzvah on the Shabbat after their thirteenth birthdays.
• The number of steps on the pyramid on the back of the American $1 Bill
• The number of original colonies the United States was founded from. The original flag had thirteen stars, one for each state. New stars have since been added whenever a new state joins the union, but the idea of adding stripes for new states was soon dropped, so the American flag to this day has thirteen horizontal stripes, six white ones and seven red ones.
• The number of guns in a gun salute to U.S. Army, Air Force and Marine Corps Major Generals, and Navy and Coast Guard Rear Admirals Upper Half.
• The number of Plutonium slugs in Fat Man, the atomic bomb dropped on Nagasaki.
• Thirteen, a 2003 movie by Catherine Hardwicke.
• Historical years: 13 A.D., 13 B.C, or 1913
• The 13th moon of Jupiter is Elara.
• Strauss and Howe named Generation X the "Thirteenth Generation".
• The number on a Hell's Angel's patch or tattoo that refers to the thirteenth letter of the alphabet, M, for "marijuana".
• 13, or "X3", is the number of the Mexican street gang Sureños. It refers to the thirteenth letter of the alphabet, M, for Mexico.

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