The number 4991
4991 is a composite number with 8 divisors. Its prime factorisation is 7 × 23 × 31. Divisors (8): 1, 7, 23, 31, 161, 217, 713, 4991.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 4991: a Harshad number: divisible by its digit sum 23.
- 2
4991 is composite. Its prime factorisation is
- 3
The divisors add up to 6144; without 4991 itself that is 1153, so 4991 is deficient (1153 is less than 4991). Euler's totient φ(4991) = 3960 numbers up to 4991 share no factor with it.
- 4
The digits of 4991 add up to 23, and repeating that until one digit is left gives the digital root 5. The Collatz sequence (halve if even, else 3n+1) takes 72 steps to reach 1.
LaTeX source of the formulas on this page
\[ 4991 = 7 \times 23 \times 31 \]
4991 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 8 |
| Sum of divisors | 6144 |
| Euler totient φ(n) | 3960 |
| Square | 24910081 |
| Cube | 124326214271 |
| Square root | 70.647010 |
| Digit sum / digital root | 23 / 5 |
| Collatz steps to 1 | 72 |
| Scientific notation | 4.991 × |
4991 in other forms
| Form | Value |
|---|---|
| In words | four thousand nine hundred and ninety-one |
| Binary (base 2) | 1001101111111 |
| Octal (base 8) | 11577 |
| Hexadecimal (base 16) | 137F |
| Base 3 | 20211212 |
| As time | 4991 seconds = 1 h 23 min 11 s |
Is 4991 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 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 5) | A number is divisible by 6 if it is divisible by both 2 and 3. |
| 7 | Yes (4991 ÷ 7 = 713) | 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 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 8) | A number is divisible by 11 if the alternating sum of the digits is a multiple of 11. |
| 12 | No (remainder 11) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 4991 a prime number?
No. 4991 = 7 × 23 × 31, so it is divisible by 7.
What are the factors of 4991?
1, 7, 23, 31, 161, 217, 713, 4991.
What is 4991 in binary?
1001101111111 (hexadecimal 137F, octal 11577).
What is the square root of 4991?
About 70.6470.
Is 4991 divisible by 3?
No. Its digits add up to 23, which is not a multiple of 3.
What is special about the number 4991?
4991 is a Harshad number: divisible by its digit sum 23.