85
85 is the atomic number of astatine — the rarest naturally occurring element in Earth's crust.
- Odd
- Composite
Where 85 fits
Why 85 is special
85's element is thought to exist as no more than a few grams across the entire planet's crust at any given time.
Factors & digit properties
- Divisors (4)
- 1, 5, 17, 85
- Prime factorisation
- 5 × 17
- Digit sum
- 13
- Digital root
- 4
Representations
- Decimal
- 85
- Binary
- 1010101
- Octal
- 125
- Hexadecimal
- 55
- Roman numeral
- LXXXV
- Scientific notation
- 8.500 × 10^1
Other mathematical patterns
- Deficient number
- Semiprime
Related numbers & connections
Mathematical relationship17 is a factor of 85 (17 × 5 = 85).
85 has factor 1717 is a factor of 85 (17 × 5 = 85).
17 is a factor of 85 (17 × 5 = 85).
View 17 →Mathematically related
- has factor17
why?
Strength 0.50, confidence "high".
Science
85 is the atomic number of astatine, the rarest naturally occurring element in Earth's crust.
DocumentedScience
Mathematics
85 factors as 5 × 17.
DocumentedMathematics
Common questions
Is 85 a prime number?
No, 85 is not prime.
What are the factors of 85?
The factors of 85 are 1, 5, 17, 85.
What is 85 in Roman numerals?
85 in Roman numerals is LXXXV.
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