The number 7981
7981 is a composite number with 4 divisors. Its prime factorisation is 23 × 347. Divisors (4): 1, 23, 347, 7981.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 7981: a semiprime: 23 × 347, the product of two primes.
- 2
7981 is composite. Its prime factorisation is
- 3
The divisors add up to 8352; without 7981 itself that is 371, so 7981 is deficient (371 is less than 7981). Euler's totient φ(7981) = 7612 numbers up to 7981 share no factor with it.
- 4
The digits of 7981 add up to 25, and repeating that until one digit is left gives the digital root 7. The Collatz sequence (halve if even, else 3n+1) takes 52 steps to reach 1.
LaTeX source of the formulas on this page
\[ 7981 = 23 \times 347 \]
7981 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 4 |
| Sum of divisors | 8352 |
| Euler totient φ(n) | 7612 |
| Square | 63696361 |
| Cube | 508360657141 |
| Square root | 89.336443 |
| Digit sum / digital root | 25 / 7 |
| Collatz steps to 1 | 52 |
| Scientific notation | 7.981 × |
7981 in other forms
| Form | Value |
|---|---|
| In words | seven thousand nine hundred and eighty-one |
| Binary (base 2) | 1111100101101 |
| Octal (base 8) | 17455 |
| Hexadecimal (base 16) | 1F2D |
| Base 3 | 101221121 |
| As time | 7981 seconds = 2 h 13 min 1 s |
Is 7981 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 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 1) | 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 5) | A number is divisible by 8 if the last three digits make a multiple of 8. |
| 9 | No (remainder 7) | 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 1) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 7981 a prime number?
No. 7981 = 23 × 347, so it is divisible by 23.
What are the factors of 7981?
1, 23, 347, 7981.
What is 7981 in binary?
1111100101101 (hexadecimal 1F2D, octal 17455).
What is the square root of 7981?
About 89.3364.
Is 7981 divisible by 3?
No. Its digits add up to 25, which is not a multiple of 3.
What is special about the number 7981?
7981 is a semiprime: 23 × 347, the product of two primes.