18 (number)

Look up eighteen in Wiktionary, the free dictionary.

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

Mathematics

18 is a semiperfect number and an abundant number. In the classification of finite simple groups, there are 18 infinite families of groups.

Although 18 and σ(18) = 39 are not coprime, 18 is known to be a solitary number. 18 is the smallest number known to have this property; for 10, 14, and 15, their status as friendly or solitary is not known.

In science

In religion and literature

As lucky or unlucky number

• 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'.^{[citation needed]}

Age 18

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. Many websites restrict adult content to visitors who claim to be at least 18 years old.

• In the United States, 18 is the:
  • Age for sexual consent in eleven states and under federal law.
  • Minimum age to purchase firearms in thirty-eight states with the exception of handguns (21 under federal law).
  • Marriageable age without parental consent except for Nebraska (19), Mississippi, (19) 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 the UK, 18 is the legal age to purchase a BBFC "18" rated film.
• In Japan, 18 is the minimum age at which one can purchase, rent, or buy tickets to R18+ rated movies or buy video games with a Z rating, although 20 is their cultural age of adulthood.

In sports

• In association football (soccer), "the 18" is a slang term for the penalty area.

References