15
15 is a triangular number, the atomic number of phosphorus, and the size of a rugby union team.
- Odd
- Composite
Where 15 fits
Why 15 is special
15's mathematical identity (triangular, the sum of 1 through 5) sits alongside a genuine sporting distinction: it's exactly two more players than a rugby league team.
Same number, different meanings
How 15 is understood across different contexts — never implying one meaning because of another.
- Mathematics
15's mathematical identity (triangular, the sum of 1 through 5) sits alongside a genuine sporting distinction: it's exactly two more players than a rugby league team.
- Science
15 is the atomic number of phosphorus, essential to DNA and to ATP, the molecule cells use to store and transfer energy.
- Sport
A rugby union team fields 15 players, compared to 13 in rugby league — one of the clearest numeric distinctions between the two codes of rugby.
Factors & digit properties
- Divisors (4)
- 1, 3, 5, 15
- Prime factorisation
- 3 × 5
- Digit sum
- 6
- Digital root
- 6
Representations
- Decimal
- 15
- Binary
- 1111
- Octal
- 17
- Hexadecimal
- f
- Roman numeral
- XV
- Scientific notation
- 1.500 × 10^1
Other mathematical patterns
- Triangular number
- Deficient number
- Hexagonal number
- Semiprime
- Lucky number (mathematical sieve)
Related numbers & connections
15 is a factor of 60 (15 × 4 = 60).
View 60 →Science
15 is the atomic number of phosphorus, essential to DNA and to ATP, the molecule cells use to store and transfer energy.
DocumentedScience
Sport
A rugby union team fields 15 players, compared to 13 in rugby league — one of the clearest numeric distinctions between the two codes of rugby.
DocumentedSport
Common questions
Is 15 a prime number?
No, 15 is not prime.
What are the factors of 15?
The factors of 15 are 1, 3, 5, 15.
What is 15 in Roman numerals?
15 in Roman numerals is XV.
About this page's data
Mathematical facts:computed directly from the number's value — nothing to source or verify externally.
Contextual records: 2 reviewer-confirmed records, sourced and reviewed before publication.
Last reviewed: 15 July 2026