The number 18981
18981 is a palindrome: it reads 18981 backwards too. Its prime factorisation is × 19 × 37. Divisors (16): 1, 3, 9, 19, 27, 37, 57, 111, 171, 333, 513, 703, 999, 2109, 6327, 18981.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 18981: a palindrome: it reads 18981 backwards too; a Harshad number: divisible by its digit sum 27.
- 2
18981 is composite. Its prime factorisation is
- 3
The divisors add up to 30400; without 18981 itself that is 11419, so 18981 is deficient (11419 is less than 18981). Euler's totient φ(18981) = 11664 numbers up to 18981 share no factor with it.
- 4
The digits of 18981 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 53 steps to reach 1.
LaTeX source of the formulas on this page
\[ 18981 = 3^{3} \times 19 \times 37 \]18981 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 16 |
| Sum of divisors | 30400 |
| Euler totient φ(n) | 11664 |
| Square | 360278361 |
| Cube | 6838443570141 |
| Square root | 137.771550 (= 3√2109) |
| Digit sum / digital root | 27 / 9 |
| Collatz steps to 1 | 53 |
| Scientific notation | 1.8981 × |
18981 in other forms
| Form | Value |
|---|---|
| In words | eighteen thousand nine hundred and eighty-one |
| Binary (base 2) | 100101000100101 |
| Octal (base 8) | 45045 |
| Hexadecimal (base 16) | 4A25 |
| Base 3 | 222001000 |
| As time | 18981 seconds = 5 h 16 min 21 s |
Is 18981 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 (18981 ÷ 3 = 6327) | 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 4) | 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 (18981 ÷ 9 = 2109) | 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 9) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 18981 a prime number?
No. 18981 = × 19 × 37, so it is divisible by 3.
What are the factors of 18981?
1, 3, 9, 19, 27, 37, 57, 111, 171, 333, 513, 703, 999, 2109, 6327, 18981.
What is 18981 in binary?
100101000100101 (hexadecimal 4A25, octal 45045).
What is the square root of 18981?
About 137.7716, exactly 3√2109.
Is 18981 divisible by 3?
Yes. Its digits add up to 27, a multiple of 3.
What is special about the number 18981?
18981 is a palindrome: it reads 18981 backwards too; a Harshad number: divisible by its digit sum 27.