The number 27991
27991 is a composite number with 4 divisors. Its prime factorisation is 23 × 1217. Divisors (4): 1, 23, 1217, 27991.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 27991: a semiprime: 23 × 1217, the product of two primes.
- 2
27991 is composite. Its prime factorisation is
- 3
The divisors add up to 29232; without 27991 itself that is 1241, so 27991 is deficient (1241 is less than 27991). Euler's totient φ(27991) = 26752 numbers up to 27991 share no factor with it.
- 4
The digits of 27991 add up to 28, and repeating that until one digit is left gives the digital root 1. The Collatz sequence (halve if even, else 3n+1) takes 121 steps to reach 1.
LaTeX source of the formulas on this page
\[ 27991 = 23 \times 1217 \]
27991 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 4 |
| Sum of divisors | 29232 |
| Euler totient φ(n) | 26752 |
| Square | 783496081 |
| Cube | 21930838803271 |
| Square root | 167.305111 |
| Digit sum / digital root | 28 / 1 |
| Collatz steps to 1 | 121 |
| Scientific notation | 2.7991 × |
27991 in other forms
| Form | Value |
|---|---|
| In words | twenty-seven thousand nine hundred and ninety-one |
| Binary (base 2) | 110110101010111 |
| Octal (base 8) | 66527 |
| Hexadecimal (base 16) | 6D57 |
| Base 3 | 1102101201 |
| As time | 27991 seconds = 7 h 46 min 31 s |
Is 27991 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 1) | 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 1) | A number is divisible by 6 if it is divisible by both 2 and 3. |
| 7 | No (remainder 5) | 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 | No (remainder 1) | 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 7) | A number is divisible by 11 if the alternating sum of the digits is a multiple of 11. |
| 12 | No (remainder 7) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 27991 a prime number?
No. 27991 = 23 × 1217, so it is divisible by 23.
What are the factors of 27991?
1, 23, 1217, 27991.
What is 27991 in binary?
110110101010111 (hexadecimal 6D57, octal 66527).
What is the square root of 27991?
About 167.3051.
Is 27991 divisible by 3?
No. Its digits add up to 28, which is not a multiple of 3.
What is special about the number 27991?
27991 is a semiprime: 23 × 1217, the product of two primes.