The number 981
981 is a composite number with 6 divisors. Its prime factorisation is × 109. Divisors (6): 1, 3, 9, 109, 327, 981.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
981 has no famous special property in the usual lists (prime, square, cube, triangular, Fibonacci, palindrome, perfect), but it is still a composite number.
- 2
981 is composite. Its prime factorisation is
- 3
The divisors add up to 1430; without 981 itself that is 449, so 981 is deficient (449 is less than 981). Euler's totient φ(981) = 648 numbers up to 981 share no factor with it.
- 4
The digits of 981 add up to 18, and repeating that until one digit is left gives the digital root 9. The Collatz sequence (halve if even, else 3n+1) takes 23 steps to reach 1.
LaTeX source of the formulas on this page
\[ 981 = 3^{2} \times 109 \]981 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 6 |
| Sum of divisors | 1430 |
| Euler totient φ(n) | 648 |
| Square | 962361 |
| Cube | 944076141 |
| Square root | 31.320920 (= 3√109) |
| Digit sum / digital root | 18 / 9 |
| Collatz steps to 1 | 23 |
| Scientific notation | 9.81 × |
981 in other forms
| Form | Value |
|---|---|
| In words | nine hundred and eighty-one |
| Roman numerals | CMLXXXI |
| Binary (base 2) | 1111010101 |
| Octal (base 8) | 1725 |
| Hexadecimal (base 16) | 3D5 |
| Base 3 | 1100100 |
| As time | 981 seconds = 16 min 21 s |
Is 981 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 (981 ÷ 3 = 327) | 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 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 5) | A number is divisible by 8 if the last three digits make a multiple of 8. |
| 9 | Yes (981 ÷ 9 = 109) | 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 2) | A number is divisible by 11 if the alternating sum of the digits is a multiple of 11. |
| 12 | No (remainder 9) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 981 a prime number?
No. 981 = × 109, so it is divisible by 3.
What are the factors of 981?
1, 3, 9, 109, 327, 981.
What is 981 in binary?
1111010101 (hexadecimal 3D5, octal 1725).
What is the square root of 981?
About 31.3209, exactly 3√109.
What is 981 in Roman numerals?
CMLXXXI.
Is 981 divisible by 3?
Yes. Its digits add up to 18, a multiple of 3.
What is special about the number 981?
It is a composite number with 6 divisors.