Number analysis
85
85 is a composite odd number that factors as 5 × 17.
85 is a composite odd number that factors as 5 × 17.
The number itself
- Value
- 85
- Digits
- 2
- Digit sum
- 13
- Reversed
- 58
- Palindrome
- No
8 + 5
Digit sum repeated until one digit remains; equals n mod 9 (with 9 for multiples of 9).
Reverses to 58.
Parity and primality
- Parity
- Odd
- Prime
- No
- Prime factorisation
- 5 × 17
- Squarefree
- Yes
- Semiprime
- Yes
- Möbius μ(n)
- 1
- Nearest primes
- 83 ← → 89
Leaves remainder 1 on division by 2.
Composite — it factors as 5 × 17.
2 distinct prime factors, 2 with multiplicity.
No prime divides it twice.
A product of exactly two primes, counted with multiplicity.
(−1) to the power of 2 distinct prime factors.
A gap of 6 between them.
Divisors
- Aliquot sum
- 23
- Classification
- Deficient
1, 5, 17, 85
The proper divisors — everything except n itself.
Its proper divisors fall short by 62.
How many integers from 1 to n share no factor with n.
Sums and additive structure
- Sum of two squares
- Yes
- Sum of three squares
- Yes
- Sum of four squares
- Yes
2² + 9² = 85 · 6² + 7² = 85
Legendre's three-square theorem allows it.
Lagrange's four-square theorem: every non-negative integer is, without exception.
Shapes and sequences
- Figurate shapes
- None
Not triangular, square, pentagonal, hexagonal, cubic, Fibonacci, Lucas, Catalan, factorial or a power of two.
Digit curiosities
- Happy number
- No
- Harshad number
- No
- Collatz trajectory
- 9 steps to 1
Summing the squares of its digits falls into the 4 → 16 → 37 → … → 4 cycle.
Not divisible by its digit sum 13.
Peaks at 256 along the way.
Written other ways
- Binary
- 1010101
- Octal
- 125
- Hexadecimal
- 55
- Base 36
- 2D
- Roman numerals
- LXXXV
- In words
- eighty-five
- Scientific notation
- 8.5 × 10^1
Is 85 a prime number?
Composite — it factors as 5 × 17.
Nearby numbers
Other numeral systems
Beyond the bases and Roman numerals above, these notations write 85 their own way.
- Greek (alphabetic)
- ΠΕʹ
- Babylonian cuneiform
- 𒐕𒎙𒐙
- Tamil
- ௮௰௫
References
Further reading: Wikipedia · Wikidata
Notations, naming and the links above come from Wikidata, whose structured data is dedicated to the public domain under CC0-1.0. Retrieved 2026-10-07.