217
CCXVII
11011001
The number 217 — factors and divisors
Deficient
217 = 7 × 31. It has 4 divisors, adding up to 256.
Its divisors, itself excluded, add up to less than the number.
Laid out as dots
It fits as 7 × 31. The more divisors, the closer to a square.
- Prime factors
- 7 × 31
- Divisors
- 1, 7, 31, 217
- Sum of divisors
- 256
- Sum without itself
- 39
- Coprime below it
- 180
- Digit sum
- 10
- Digital root
- 1
- Roman numeral
- CCXVII
- Binary
- 11011001
- Octal
- 331
- Hexadecimal
- D9
- Base 36
- 61
- Bits
- 8 bits
- Collatz steps
- 26 steps · peaks at 736
- Prime before
- 211
- Prime after
- 223
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 217 a prime number?
No. It breaks down into 7 × 31.
Q. What are the divisors of 217?
1, 7, 31, 217 — 4 divisors in all, adding up to 256.
Q. How is 217 written in binary?
11011001, which is 8 bits. In hexadecimal it is D9.
Q. How many Collatz steps does 217 take?
It reaches 1 in 26, peaking at 736 on the way.