31
31 is a prime number, the atomic number of gallium, and the length of seven calendar months.
- Odd
- Prime
Where 31 fits
Why 31 is special
31 forms a twin-prime pair with 29, and separately is the longest a calendar month ever gets.
Same number, different meanings
How 31 is understood across different contexts — never implying one meaning because of another.
- Mathematics
31 forms a twin-prime pair with 29, and separately is the longest a calendar month ever gets.
- Science
31 is the atomic number of gallium, a metal with an unusually low melting point — just above room temperature.
- Everyday life
January, March, May, July, August, October and December each have 31 days — seven of the twelve calendar months.
31 is part of
Factors & digit properties
- Divisors (2)
- 1, 31
- Prime factorisation
- 31
- Digit sum
- 4
- Digital root
- 4
Representations
- Decimal
- 31
- Binary
- 11111
- Octal
- 37
- Hexadecimal
- 1f
- Roman numeral
- XXXI
- Scientific notation
- 3.100 × 10^1
Other mathematical patterns
Related numbers & connections
31 is a factor of 62 (31 × 2 = 62).
View 62 →29 and 31 are twin primes — two primes exactly two apart.
View 29 →Science
31 is the atomic number of gallium, a metal with an unusually low melting point — just above room temperature.
DocumentedScience
Everyday life
January, March, May, July, August, October and December each have 31 days — seven of the twelve calendar months.
DocumentedEveryday life
Common questions
Is 31 a prime number?
Yes, 31 is prime — it has exactly two positive divisors: 1 and itself.
What are the factors of 31?
The factors of 31 are 1, 31.
What is 31 in Roman numerals?
31 in Roman numerals is XXXI.
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