221
CCXXI
11011101
The number 221 — factors and divisors
Deficient
221 = 13 × 17. It has 4 divisors, adding up to 252.
Its divisors, itself excluded, add up to less than the number.
Laid out as dots
It fits as 13 × 17. The more divisors, the closer to a square.
- Prime factors
- 13 × 17
- Divisors
- 1, 13, 17, 221
- Sum of divisors
- 252
- Sum without itself
- 31
- Coprime below it
- 192
- Digit sum
- 5
- Digital root
- 5
- Roman numeral
- CCXXI
- Binary
- 11011101
- Octal
- 335
- Hexadecimal
- DD
- Base 36
- 65
- Bits
- 8 bits
- Collatz steps
- 114 steps · peaks at 9,232
- 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 221 a prime number?
No. It breaks down into 13 × 17.
Q. What are the divisors of 221?
1, 13, 17, 221 — 4 divisors in all, adding up to 252.
Q. How is 221 written in binary?
11011101, which is 8 bits. In hexadecimal it is DD.
Q. How many Collatz steps does 221 take?
It reaches 1 in 114, peaking at 9,232 on the way.