18
18 is an even, composite number. 18 does not yet have enough sourced significance to earn a full editorial profile — its mathematical properties below are fully computed and accurate.
- Even
- Composite
Where 18 fits
Why 18 is special
18 is mathematically notable: 18 is evenly divisible by the sum of its own digits.
Same number, different meanings
How 18 is understood across different contexts — never implying one meaning because of another.
- Mathematics
18 is mathematically notable: 18 is evenly divisible by the sum of its own digits.
- Science
18 is the atomic number of argon, the third most abundant gas in Earth's atmosphere (about 0.93%) and an inert noble gas used in incandescent light bulbs and welding to prevent oxidation.
- Sport
A standard round of golf consists of 18 holes — the reason 'the 19th hole' is a well-known golfing idiom for the clubhouse bar, humorously extending an 18-hole round by one more notional hole.
- Law & regulation
18 is the most common age of legal adulthood (the age of majority) across countries worldwide, though the exact threshold and its legal consequences genuinely vary by jurisdiction — some countries set it at 16, 19, 20 or 21 for some or all purposes.
Factors & digit properties
- Divisors (6)
- 1, 2, 3, 6, 9, 18
- Prime factorisation
- 2 × 3^2
- Digit sum
- 9
- Digital root
- 9
Representations
- Decimal
- 18
- Binary
- 10010
- Octal
- 22
- Hexadecimal
- 12
- Roman numeral
- XVIII
- Scientific notation
- 1.800 × 10^1
Other mathematical patterns
- Abundant number
- Harshad (Niven) number
- Lucas number
Related numbers & connections
18 (a standard golf round) and 19 (the 'clubhouse' 19th hole) are consecutive integers connected by the same golfing idiom.
View 19 →Nearby in a sequence
- is adjacent to19
why?
Strength 0.50, confidence "high".
Science
18 is the atomic number of argon, the third most abundant gas in Earth's atmosphere (about 0.93%) and an inert noble gas used in incandescent light bulbs and welding to prevent oxidation.
DocumentedScience
Sport
A standard round of golf consists of 18 holes — the reason 'the 19th hole' is a well-known golfing idiom for the clubhouse bar, humorously extending an 18-hole round by one more notional hole.
DocumentedSport
Law & regulation
18 is the most common age of legal adulthood (the age of majority) across countries worldwide, though the exact threshold and its legal consequences genuinely vary by jurisdiction — some countries set it at 16, 19, 20 or 21 for some or all purposes.
Widely documentedLaw & regulation
Common questions
Is 18 a prime number?
No, 18 is not prime.
What are the factors of 18?
The factors of 18 are 1, 2, 3, 6, 9, 18.
What is 18 in Roman numerals?
18 in Roman numerals is XVIII.
About this page's data
Mathematical facts:computed directly from the number's value — nothing to source or verify externally.
Contextual records: 3 reviewer-confirmed records, sourced and reviewed before publication.
Last reviewed: 15 July 2026