209
CCIX
11010001
The number 209 — factors and divisors
Deficient
209 = 11 × 19. It has 4 divisors, adding up to 240.
Its divisors, itself excluded, add up to less than the number.
Laid out as dots
It fits as 11 × 19. The more divisors, the closer to a square.
- Prime factors
- 11 × 19
- Divisors
- 1, 11, 19, 209
- Sum of divisors
- 240
- Sum without itself
- 31
- Coprime below it
- 180
- Digit sum
- 11
- Digital root
- 2
- Roman numeral
- CCIX
- Binary
- 11010001
- Octal
- 321
- Hexadecimal
- D1
- Base 36
- 5T
- Bits
- 8 bits
- Collatz steps
- 39 steps · peaks at 628
- Prime before
- 199
- Prime after
- 211
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 209 a prime number?
No. It breaks down into 11 × 19.
Q. What are the divisors of 209?
1, 11, 19, 209 — 4 divisors in all, adding up to 240.
Q. How is 209 written in binary?
11010001, which is 8 bits. In hexadecimal it is D1.
Q. How many Collatz steps does 209 take?
It reaches 1 in 39, peaking at 628 on the way.