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.[2]
  • 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.[3]
  • 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'.[4]
  • 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.[5]

Age 18Edit

In most countries, 18 is the age of majority, in which a minor becomes a legal adult. It is also the voting age, marriageable age, drinking age and smoking age in most countries, though sometimes these ages are different than the age of majority.

  • In the United States, 18 is the:
    • Age for sexual consent in eleven states and under federal law.[6]
    • Minimum age to purchase firearms in thirty-eight states with the exception of handguns (21 under federal law).[7]
    • Marriageable age without parental consent except for Nebraska (19), Mississippi and Puerto Rico (21).
    • The minimum age at which one can purchase, rent, or buy tickets to NC-17-rated films or buy video games with an Adults Only rating.

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. ^ Benjaminson, Chani. "What is the reason for the custom to give money gifts in multiples of 18 -- 18, 36, 54, etc.?". Chabad.org. Archived from the original on 2007-12-27. Retrieved January 19, 2022.
  3. ^ 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
  4. ^ 言必有「中」:「十八」「實發」 人見人愛. 文匯報. Accessed 2015-01-12. Archived 2015-01-15.
  5. ^ "Chai, Its Meaning and Significance | Shiva, Jewish Mourning". www.shiva.com. Retrieved 2020-11-18.
  7. ^ "Minimum Age". Giffords.
  8. ^ "18".
  9. ^ "318".
  10. ^ "Eighteen One-Name Study". One-name.org. 2012-01-13. Archived from the original on 2013-05-07. Retrieved 2013-08-02.