18 (number)

18 (eighteen) is the natural number following 17 and preceding 19.

← 17 18 19 →
Numeral systemoctodecimal
Factorization2 × 32
Divisors1, 2, 3, 6, 9, 18
Greek numeralΙΗ´
Roman numeralXVIII

In mathematicsEdit

In scienceEdit


In religion and literatureEdit

  • The Hebrew word for "life" is חי (chai), which has a numerical value of 18. Consequently, the custom has arisen in Jewish circles to give donations and monetary gifts in multiples of 18 as an expression of blessing for long life.
  • In Judaism, in the Talmud; Pirkei Avot (5:25), Rabbi Yehudah ben Teime gives the age of 18 as the appropriate age to get married ("Ben shmonah esra lechupah", at eighteen years old to the Chupah (marriage canopy)). (See Coming of age, Age of majority).
  • Shemoneh Esrei (sh'MOH-nuh ES-ray) is a prayer that is the center of any Jewish religious service. Its name means "eighteen". The prayer is also known as the Amidah.
  • In Ancient Roman custom the number 18 can symbolise a blood relative.
  • Joseph Heller's novel Catch-22 was originally named Catch-18 because of the Hebrew meaning of the number, but was amended to the published title to avoid confusion with another war novel, Mila 18.[2]
  • There are 18 chapters in the Bhagavad Gita, which is contained in the Mahabharata, which has 18 books. The Kurukshetra War which the epic depicts, is between 18 armies (11 on the Kuru side, 7 on the Pandava). The war itself lasts for 18 days. In the other Hindu epic, the Ramayana, the war between Rama and the demons also lasted 18 days.
  • In Babism the first 18 disciples of the Báb were known as the Letters of the Living.

As lucky or unlucky numberEdit

  • In Chinese tradition, 18 pronounced 十八 (shí bā) and is considered a lucky number due to similarity with 實發 (shì fā) 'definitely get rich', 'to get rich for sure'.[3]
  • According to applications of numerology in Judaism, the letters of the word chai ("living") add up to 18. Thus, 18 is considered a lucky number and many gifts for B'nai Mitzvot and weddings are in $18 increments.[4]

Age 18Edit

In most countries, 18 is the age of majority (adulthood) and also the voting age.

In eleven states of the United States, 18 is the age of sexual consent.

In most US states and pursuant to federal law, 18 is the minimum age to purchase firearms (with the exception of handguns) 18 is also the minimum age to get married without parental consent.

It is the minimum age at which one can purchase, rent, or buy tickets to NC-17-rated films or buy video games with an AO rating.

It is also the age of sexual consent under U.S. federal law (although this law only applies in circumstances involving transportation or transaction between different states or outside the United States).[5]

In addition, Pennsylvania has a corruption of minors law that makes the de facto age of consent there 18.[6] This is also the case in some jurisdictions outside the United States,[7] including Canada.[8][9]

In sportsEdit

In other fieldsEdit

Eighteen is also:

See alsoEdit


  1. ^ "Sloane's A005835 : Pseudoperfect (or semiperfect) numbers". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-05-31.
  2. ^ N James. The Early Composition History of Catch-22. In Biographies of Books: The Compositional Histories of Notable American Writings, J Barbour, T Quirk (edi.) pp. 262-90. Columbia: University of Missouri Press, 1996
  3. ^ 言必有「中」:「十八」「實發」 人見人愛. 文匯報. Accessed 2015-01-12. Archived 2015-01-15.
  4. ^ "Chai, Its Meaning and Significance | Shiva, Jewish Mourning". www.shiva.com. Retrieved 2020-11-18.
  5. ^ "The US Federal Age of Sexual Consent". SOL Research. Retrieved 2013-08-02.
  6. ^ "Age Of Consent By State". Age-of-consent.info. Archived from the original on 2011-04-17. Retrieved 2013-08-02.
  7. ^ "Worldwide Ages of Consent". Avert.org. Retrieved 2013-08-02.
  8. ^ CANADA'S LEGAL AGE OF CONSENT TO SEXUAL ACTIVITY Revised 12 April 2001: "Section 153 now prohibits "sexual interference" or "invitation to sexual touching," in respect of a young person over 14 but under 18, where the accused is in a relationship of trust or authority towards the complainant or the complainant is in a relationship of dependency with the accused."
  9. ^ Government of Canada - Age of Consent to Sexual Activity: "the age of consent is 18 years where the sexual activity "exploits" the young person -- when it involves prostitution, pornography or occurs in a relationship of authority, trust or dependency (e.g., with a teacher, coach or babysitter). Sexual activity can also be considered exploitative based on the nature and circumstances of the relationship, e.g., the young person's age, the age difference between the young person and their partner, how the relationship developed (quickly, secretly, or over the Internet) and how the partner may have controlled or influenced the young person."
  10. ^ [1]
  11. ^ [2]
  12. ^ "Eighteen One-Name Study". One-name.org. 2012-01-13. Archived from the original on 2013-05-07. Retrieved 2013-08-02.