The number 18921
18921 is a composite number with 16 divisors. Its prime factorisation is 3 × 7 × 17 × 53. Divisors (16): 1, 3, 7, 17, 21, 51, 53, 119, 159, 357, 371, 901, 1113, 2703, 6307, 18921.
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How to work it out
- 1
What is special about 18921: a Harshad number: divisible by its digit sum 21.
- 2
18921 is composite. Its prime factorisation is
- 3
The divisors add up to 31104; without 18921 itself that is 12183, so 18921 is deficient (12183 is less than 18921). Euler's totient φ(18921) = 9984 numbers up to 18921 share no factor with it.
- 4
The digits of 18921 add up to 21, and repeating that until one digit is left gives the digital root 3. The Collatz sequence (halve if even, else 3n+1) takes 105 steps to reach 1.
LaTeX source of the formulas on this page
\[ 18921 = 3 \times 7 \times 17 \times 53 \]
18921 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 16 |
| Sum of divisors | 31104 |
| Euler totient φ(n) | 9984 |
| Square | 358004241 |
| Cube | 6773798243961 |
| Square root | 137.553626 |
| Digit sum / digital root | 21 / 3 |
| Collatz steps to 1 | 105 |
| Scientific notation | 1.8921 × |
18921 in other forms
| Form | Value |
|---|---|
| In words | eighteen thousand nine hundred and twenty-one |
| Binary (base 2) | 100100111101001 |
| Octal (base 8) | 44751 |
| Hexadecimal (base 16) | 49E9 |
| Base 3 | 221221210 |
| As time | 18921 seconds = 5 h 15 min 21 s |
Is 18921 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 (18921 ÷ 3 = 6307) | 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 | Yes (18921 ÷ 7 = 2703) | 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 1) | A number is divisible by 8 if the last three digits make a multiple of 8. |
| 9 | No (remainder 3) | 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 1) | 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 18921 a prime number?
No. 18921 = 3 × 7 × 17 × 53, so it is divisible by 3.
What are the factors of 18921?
1, 3, 7, 17, 21, 51, 53, 119, 159, 357, 371, 901, 1113, 2703, 6307, 18921.
What is 18921 in binary?
100100111101001 (hexadecimal 49E9, octal 44751).
What is the square root of 18921?
About 137.5536.
Is 18921 divisible by 3?
Yes. Its digits add up to 21, a multiple of 3.
What is special about the number 18921?
18921 is a Harshad number: divisible by its digit sum 21.