The number 17991
17991 is a composite number with 6 divisors. Its prime factorisation is × 1999. Divisors (6): 1, 3, 9, 1999, 5997, 17991.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
17991 has no famous special property in the usual lists (prime, square, cube, triangular, Fibonacci, palindrome, perfect), but it is still a composite number.
- 2
17991 is composite. Its prime factorisation is
- 3
The divisors add up to 26000; without 17991 itself that is 8009, so 17991 is deficient (8009 is less than 17991). Euler's totient φ(17991) = 11988 numbers up to 17991 share no factor with it.
- 4
The digits of 17991 add up to 27, and repeating that until one digit is left gives the digital root 9. The Collatz sequence (halve if even, else 3n+1) takes 141 steps to reach 1.
LaTeX source of the formulas on this page
\[ 17991 = 3^{2} \times 1999 \]17991 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 6 |
| Sum of divisors | 26000 |
| Euler totient φ(n) | 11988 |
| Square | 323676081 |
| Cube | 5823256373271 |
| Square root | 134.130533 (= 3√1999) |
| Digit sum / digital root | 27 / 9 |
| Collatz steps to 1 | 141 |
| Scientific notation | 1.7991 × |
17991 in other forms
| Form | Value |
|---|---|
| In words | seventeen thousand nine hundred and ninety-one |
| Binary (base 2) | 100011001000111 |
| Octal (base 8) | 43107 |
| Hexadecimal (base 16) | 4647 |
| Base 3 | 220200100 |
| As time | 17991 seconds = 4 h 59 min 51 s |
Is 17991 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 | Yes (17991 ÷ 3 = 5997) | A number is divisible by 3 if the digits add up to a multiple of 3. |
| 4 | No (remainder 3) | 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 3) | A number is divisible by 6 if it is divisible by both 2 and 3. |
| 7 | No (remainder 1) | 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 7) | A number is divisible by 8 if the last three digits make a multiple of 8. |
| 9 | Yes (17991 ÷ 9 = 1999) | 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 6) | A number is divisible by 11 if the alternating sum of the digits is a multiple of 11. |
| 12 | No (remainder 3) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 17991 a prime number?
No. 17991 = × 1999, so it is divisible by 3.
What are the factors of 17991?
1, 3, 9, 1999, 5997, 17991.
What is 17991 in binary?
100011001000111 (hexadecimal 4647, octal 43107).
What is the square root of 17991?
About 134.1305, exactly 3√1999.
Is 17991 divisible by 3?
Yes. Its digits add up to 27, a multiple of 3.
What is special about the number 17991?
It is a composite number with 6 divisors.