85
LXXXV
1010101
The number 85 — factors and divisors
Deficient
85 = 5 × 17. It has 4 divisors, adding up to 108.
Its divisors, itself excluded, add up to less than the number.
Laid out as dots
It fits as 5 × 17. The more divisors, the closer to a square.
- Prime factors
- 5 × 17
- Divisors
- 1, 5, 17, 85
- Sum of divisors
- 108
- Sum without itself
- 23
- Coprime below it
- 64
- Digit sum
- 13
- Digital root
- 4
- Roman numeral
- LXXXV
- Binary
- 1010101
- Octal
- 125
- Hexadecimal
- 55
- Base 36
- 2D
- Bits
- 7 bits
- Collatz steps
- 9 steps · peaks at 256
- Prime before
- 83
- Prime after
- 89
The grid
Ten per row, twenty rows. The filled cells are primes — you can see the multiples of 2 and 5 drop out in columns.
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Numbers either side
How to read this
- The prime factors are what the number is made of. The count and sum of divisors both follow from them.
- Add the divisors, take the number away, and you get perfect, abundant or deficient.
- The length of the binary form is the bit count. 255 taking eight digits is what a byte is.
- Collatz: halve it if even, triple it and add one if odd. The count is how many moves reach 1.
Frequently asked questions
Q. Is 85 a prime number?
No. It breaks down into 5 × 17.
Q. What are the divisors of 85?
1, 5, 17, 85 — 4 divisors in all, adding up to 108.
Q. How is 85 written in binary?
1010101, which is 7 bits. In hexadecimal it is 55.
Q. How many Collatz steps does 85 take?
It reaches 1 in 9, peaking at 256 on the way.