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 child Jesus having received the Magi on his thirteenth day of life.

In the Jewish tradition, 13 signifies the age of maturity, a 13 year old Jew is said to be Bar mitzvah. It is also the number of the tribes (of them 11 are the sons of Jacob and two more are named after the two sons of Joseph) and appears in other places in the Hebrew Bible though not as often as other famous biblical numbers such as 7 and 12. In fact, one could say that for Jews, 13 is more of a lucky number than an unlucky one.

In the Sikh religion, the number 13 is considered a special number since 13 is tera in punjabi which also means yours. When Guru Nanak Dev Ji had a job of counting stocks of items. When he was counting he counted from 1 to 13 (in Punjabi) as normal but after 13 he would just repeat "tera" for all the items since all the items were in fact God's since God created them. When somebody heard this while passing and Guru Nanak Dev Ji was confronted about this his records were checked, it was a miracle since they were all perfect, yet he never seemed to count the items properly.

Modern day witches have reclaimed the number 13 as a lucky and significant number. This may be similar to witches reclaiming other previously negative terms and ideas associated with witchcraft, such as black cats, brooms, and even the term witch itself. In modern day Wicca, thirteen is considered the maximum size of a coven, and in some traditions the ideal number of members. In Gardnerian Wicca, the ideal coven has thirteen members.

Amongst some Chinese people, it is regarded as a lucky number because it is sounds similar to "實生", which means "must be alive". But this belief is not universal, or even known to all Chinese. Also, 13 is regarded as unlucky by those Chinese under the influence of foreign cultures.

In The Hitchhiker's Guide to the Galaxy, "What is six times nine" is posed as the question to the answer to life, the universe and everything of 42. This happens to be true in base 13.

Friday The 13th is remembered because Knights Templar  the supposed protectors of the Grail were massacred. [Knight Templar very intrinsic to this adventure]

Some also say that the arrest of Jaques de Molay, Grand Master of the Knights Templar, and 60 of his senior knights on Friday, October 13, 1307 by King Philip IV of France, is the origin of this superstition. That day thousands of Templars were arrested and subsequently tortured. They then 'confessed' and were executed. From that day on, Friday the 13th was considered as an evil and unlucky day.

Strangely, there is evidence to suggest that Friday the 13th is actually unlucky for some. Psychologists have found that some people are especially likely to have accidents or fall ill on Friday the 13th. This has been attributed to such people feeling a heightened state of anxiety on that day. The Stress Management Center and Phobia Institute in Asheville, North Carolina estimates that in the United States alone, $800 or $900 million is lost in business each Friday the 13th because some people will not travel or go to work. [1]

The date is also well-known in the motorcycle (biker) community: since 1981, motorcycle enthusiasts and vendors gather every Friday the 13th in Port Dover, Ontario, Canada. This tradition started on November 13, 1981 by Chris Simons as a gathering of approximately 25 friends. The event has grown substantially, with an estimated 100,000 people attending in August 2004, as well as music bands, vendors, a bike show, etc. [2]

In the Spanish-speaking world, it is Tuesday the 13th (as well as Tuesdays in general) that brings bad luck; a proverb runs En martes, ni te cases ni te embarques (on Tuesday, neither get married nor start a journey).

Thirteen is the 6th smallest prime number; the next is seventeen. 13 is the second Wilson prime. 13 is the fifth Mersenne prime exponent, yielding 8191. 13 is also the third lucky prime.

13 is the second star number and the seventh Fibonacci number. There are 13 Archimedean solids.

13 goes into 999,999 exactly 76,923 times, so vulgar 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.

13 is the only positive integer that is the fourth root of the sum of the squares of two successive positive integers (119 and 120)

In science

• The atomic number of aluminium
• The number of dimensions in some theories of relativity

In astronomy,

Messier object M13, a magnitude 7.0 globular cluster in the constellation Hercules, also known as the Hercules cluster. It is one of the brightest and best-known of the globular clusters.

The New General Catalogue object NGC 13, a spiral galaxy in the constellation Andromeda

The Saros number of the solar eclipse series which began on -2561 September 12 and ended on -1046 March 9. The duration of Saros series 13 was 1514.5 years, and it contained 85 solar eclipses.

The Saros number of the lunar eclipse series which began on -2313 May 20 and ended on -1015 July 6. The duration of Saros series 13 was 1298.1 years, and it contained 73 lunar eclipses.

The 13th moon of Jupiter is Elara.

The known universe is currently thought to be about 13.7 billion years old, with an error of about one percent.

13What makes the difference? It is in your mind.

Thirteen is:

• The number of loaves in a "baker's dozen".
• The ASCII and Unicode value for carriage return.
• "Unlucky for some", according to bingo callers.
• The number of players in a rugby league team.
• The age of maturity in Jewish tradition. A boy gets his bar mitzvah on the Shabbat after his thirteenth birthday.
• The number of principles of Jewish faith according to Maimonides
• In Jewish tradition, God has 13 Attributes of Mercy
• 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.
• A U.S. 1 Dollar note has:
  • 13 levels of the truncated pyramid,
  • 13 stripes on the flag,
  • 13 letters in "E Pluribus Unum",
  • 13 stars above the Eagle,
  • 13 leaves on the olive branch,
  • 13 arrows held by the Eagle, and
  • 13 bars on the shield.
• 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.
• 13 is a 1999 album by British band Blur
• 13 is a 2005 album by American band Six Feet Under
• In the title of the movies:
  • Thirteen, a 2003 movie by Catherine Hardwicke;
  • Thirteen Days, a 2000 movie about the Cuban Missile Crisis;
  • The Thirteenth Floor a 1999 movie;
  • 13 Going On 30, a movie starring Jennifer Garner in which the protagonist is 13 years old at the outset;
  • Apollo 13, a movie starring Tom Hanks (13th Apollo mission);
  • Thir13en Ghosts, a 2001 horror movie starring Tony Shalhoub (a remake of 1960's 13 Ghosts, which starred Charles Herbert);
  • 13 Conversations About One Thing, starring Matthew McConaughey;
  • Assault on Precinct 13 (1976 movie), an action movie starring Austin Stoker;
  • Assault on Precinct 13 (2005 movie), a loose remake of the 1976 movie, starring Ethan Hawke and Laurence Fishburne
  • Dementia 13, a horror movie directed by Francis Ford Coppola; and
  • Ward 13, an animated short movie.
• 13 Engines, a Canadian alternative rock band.
• 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.
• In rugby union one of the centres, most often but not always the outside centre, wears the 13 shirt.
• Historical years: A.D. 13, 13 B.C., or 1913.
• In the episode of King of the Hill when Connie has her first period and she goes with Hank to the Megalomart to buy tampons, the feminine hygiene items are in Aisle 13. This was changed to Aisle 8A when the episode reran.
• Israel Naval covert unit - Shayetet 13
• A song by the band Osker, also the title of a song by the band Bigwig