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
- Scientific notation
- 8.500 × 10^1
Roman numerals
L X X X V
Binary
1 0 1 0 1 0 1
1 × 64 + 0 × 32 + 1 × 16 + 0 × 8 + 1 × 4 + 0 × 2 + 1 × 1 = 85
Octal
1 2 5
1 × 64 + 2 × 8 + 5 × 1 = 85
Hexadecimal
5 5
5 × 16 + 5 × 1 = 85
Read as powers of two: 64 + 16 + 4 + 1 = 85.
In historical numeral systems
Egyptian
8 hobbles, 5 strokes
8 × 10 + 5 × 1 = 85. The signs are simply repeated and added; where they sit on the line is a matter of layout, not value.
Babylonian
1 vertical wedge (sixties place), 2 corner wedges + 5 vertical wedges (units place)
1 × 60 + 25 = 85. Places are separated by a space on the tablet, with the higher place written first.
Greek (Ionic)
pi, then epsilon, marked as a numeral
pi-epsilon + keraia
pi + epsilon written in descending order and added — the letters carry their values wherever they stand, so this is addition, not place value.
Hebrew numerals
pe, then he
pe-he
pe (80) + he (5) = 85, written in descending order.
Chinese numerals
bā shí wǔ
bā shí wǔ
八 before 十 multiplies it: 8 tens. 五 after it adds 5. The written form mirrors the arithmetic — "bā shí wǔ". The financial (anti-fraud) form is 捌拾伍.
Maya
4 dots (upper, twenties place) over 1 bar (lower, units place)
4 × 20 + 5 = 85. Places stack vertically with the smallest at the bottom, so the upper group is worth twenty times the lower.
Systems that simply cannot reach this value are left out. Where a script needs a font most readers do not have, the reading is given instead of the glyphs — see number systems for each system in full.
Other mathematical patterns
- Deficient number
- Semiprime
Related numbers & connections
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