18 (number)

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

In speech, the numbers 18 and 80 are sometimes confused. When carefully enunciated, they differ in which syllable is stressed: 18 /eɪtˈtiːn/ vs 80 /ˈeɪti/. However, in dates such as 1864, or when contrasting numbers in the teens, such as 17, 18, 19, the stress shifts to the first syllable: 18 /ˈeɪttiːn/. In some dialects, such as General American, there is little confusion because the single t sound in 80 becomes a d-like flap [ɾ], whereas the double t sound in 18 does not.

In mathematics

Eighteen is a composite number, its proper 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. Eighteen is the first inverted square-prime of the form p·q².

It is a heptagonal number, and as the sum of the first three pentagonal numbers, it is a pentagonal pyramidal number. It is also the sum of the totient function for the first seven integers. It is the sixth lucas number.

Birthday

A birthday is an occasion when a person or institution celebrates the anniversary of their birth. Birthdays are celebrated in numerous cultures, often with a gift, party, or rite of passage.

Many religions celebrate the birth of their founders with special holidays (e.g. Christmas, Buddha's Birthday).

Note the distinction between birthday and birthdate: The former, other than February 29, occurs each year (e.g. May 11), while the latter is the exact date a person was born (e.g., May 11, 1998).

Legal conventions

In most legal systems, one becomes designated as an adult on a particular birthday (usually between 12 and 21), and reaching age-specific milestones confers particular rights and responsibilities. At certain ages, one may become eligible to leave full-time education, or become subject to military conscription or to enlist in the military, to consent to sexual intercourse, to marry, to marry without parental consent, to vote, to run for elected office, to legally purchase (or consume) alcohol and tobacco products, to purchase lottery tickets, or to obtain a driver's licence. The age of majority is the age when minors cease to legally be considered children and assume control over their persons, actions, and decisions, thereby terminating the legal control and legal responsibilities of their parents or guardian over and for them. Most countries set majority between 18 to 21.

2016

2016 (MMXVI) is the current year, and is a leap year starting on Friday (dominical letter CB) of the Gregorian calendar, the 2016th year of the Common Era (CE) and Anno Domini (AD) designations, the 16th year of the 3rd millennium, the 16th year of the 21st century, and the 7th year of the 2010s decade.

2016 has been designated as:

Events

January

November 18

November 18 is the 322nd day of the year (323rd in leap years) in the Gregorian calendar. There are 43 days remaining until the end of the year.

Events