Eighteen is the tenth
composite number, its
divisors being
1,
2,
3,
6 and
9. Three of these divisors (3, 6 and 9) add up to 18, hence 18 is a
semiperfect number.[1] Eighteen is the first inverted square-prime of the form p·q2.
It is an
abundant number, as the sum of its proper divisors is greater than itself (1+2+3+6+9 = 21). It is known to be a
solitary number, despite not being
coprime to this sum.
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.[3]
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.
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.[4]
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
Chinese tradition, 18 is 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'.[5]
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.[6]
^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
Eighteen is the tenth
composite number, its
divisors being
1,
2,
3,
6 and
9. Three of these divisors (3, 6 and 9) add up to 18, hence 18 is a
semiperfect number.[1] Eighteen is the first inverted square-prime of the form p·q2.
It is an
abundant number, as the sum of its proper divisors is greater than itself (1+2+3+6+9 = 21). It is known to be a
solitary number, despite not being
coprime to this sum.
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.[3]
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.
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.[4]
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
Chinese tradition, 18 is 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'.[5]
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.[6]
^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