191
CXCI
10111111
The number 191 — factors and divisors
Deficient
191 is a prime: only 1 and itself divide it. The prime before is 181, the next is 193.
Its divisors, itself excluded, add up to less than the number.
Families it belongs to
Prime
Nothing divides it but 1 and itself.
Laid out as dots
It only fits in one row. Having no other rectangle is what being prime means.
- Prime factors
- It does not break down further
- Divisors
- 1, 191
- Sum of divisors
- 192
- Sum without itself
- 1
- Coprime below it
- 190
- Digit sum
- 11
- Digital root
- 2
- Roman numeral
- CXCI
- Binary
- 10111111
- Octal
- 277
- Hexadecimal
- BF
- Base 36
- 5B
- Bits
- 8 bits
- Collatz steps
- 44 steps · peaks at 4,372
- Prime before
- 181
- Prime after
- 193
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 191 a prime number?
Yes. Nothing divides it but 1 and itself.
Q. What are the divisors of 191?
1, 191 — 2 divisors in all, adding up to 192.
Q. How is 191 written in binary?
10111111, which is 8 bits. In hexadecimal it is BF.
Q. How many Collatz steps does 191 take?
It reaches 1 in 44, peaking at 4,372 on the way.