The number 221
221 is a composite number with 4 divisors. Its prime factorisation is 13 × 17. Divisors (4): 1, 13, 17, 221.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 221: a semiprime: 13 × 17, the product of two primes.
- 2
221 is composite. Its prime factorisation is
- 3
The divisors add up to 252; without 221 itself that is 31, so 221 is deficient (31 is less than 221). Euler's totient φ(221) = 192 numbers up to 221 share no factor with it.
- 4
The digits of 221 add up to 5, and repeating that until one digit is left gives the digital root 5. The Collatz sequence (halve if even, else 3n+1) takes 114 steps to reach 1.
LaTeX source of the formulas on this page
\[ 221 = 13 \times 17 \]
221 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 4 |
| Sum of divisors | 252 |
| Euler totient φ(n) | 192 |
| Square | 48841 |
| Cube | 10793861 |
| Square root | 14.866069 |
| Digit sum / digital root | 5 / 5 |
| Collatz steps to 1 | 114 |
| Scientific notation | 2.21 × |
221 in other forms
| Form | Value |
|---|---|
| In words | two hundred and twenty-one |
| Roman numerals | CCXXI |
| Binary (base 2) | 11011101 |
| Octal (base 8) | 335 |
| Hexadecimal (base 16) | DD |
| Base 3 | 22012 |
| As time | 221 seconds = 3 min 41 s |
Is 221 divisible by 2 to 12?
| Divisor | Answer | Rule |
|---|---|---|
| 2 | No (remainder 1) | A number is divisible by 2 if the last digit is even (0, 2, 4, 6, 8). |
| 3 | No (remainder 2) | A number is divisible by 3 if the digits add up to a multiple of 3. |
| 4 | No (remainder 1) | A number is divisible by 4 if the last two digits make a multiple of 4. |
| 5 | No (remainder 1) | A number is divisible by 5 if the last digit is 0 or 5. |
| 6 | No (remainder 5) | A number is divisible by 6 if it is divisible by both 2 and 3. |
| 7 | No (remainder 4) | A number is divisible by 7 if double the last digit and subtract it from the rest: the result is a multiple of 7. |
| 8 | No (remainder 5) | A number is divisible by 8 if the last three digits make a multiple of 8. |
| 9 | No (remainder 5) | A number is divisible by 9 if the digits add up to a multiple of 9. |
| 10 | No (remainder 1) | A number is divisible by 10 if the last digit is 0. |
| 11 | No (remainder 1) | A number is divisible by 11 if the alternating sum of the digits is a multiple of 11. |
| 12 | No (remainder 5) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 221 a prime number?
No. 221 = 13 × 17, so it is divisible by 13.
What are the factors of 221?
1, 13, 17, 221.
What is 221 in binary?
11011101 (hexadecimal DD, octal 335).
What is the square root of 221?
About 14.8661.
What is 221 in Roman numerals?
CCXXI.
Is 221 divisible by 3?
No. Its digits add up to 5, which is not a multiple of 3.
What is special about the number 221?
221 is a semiprime: 13 × 17, the product of two primes.