The number 16821
16821 is a composite number with 16 divisors. Its prime factorisation is × 7 × 89. Divisors (16): 1, 3, 7, 9, 21, 27, 63, 89, 189, 267, 623, 801, 1869, 2403, 5607, 16821.
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How to work it out
- 1
16821 has no famous special property in the usual lists (prime, square, cube, triangular, Fibonacci, palindrome, perfect), but it is still a composite number.
- 2
16821 is composite. Its prime factorisation is
- 3
The divisors add up to 28800; without 16821 itself that is 11979, so 16821 is deficient (11979 is less than 16821). Euler's totient φ(16821) = 9504 numbers up to 16821 share no factor with it.
- 4
The digits of 16821 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 97 steps to reach 1.
LaTeX source of the formulas on this page
\[ 16821 = 3^{3} \times 7 \times 89 \]16821 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 16 |
| Sum of divisors | 28800 |
| Euler totient φ(n) | 9504 |
| Square | 282946041 |
| Cube | 4759435355661 |
| Square root | 129.695798 (= 3√1869) |
| Digit sum / digital root | 18 / 9 |
| Collatz steps to 1 | 97 |
| Scientific notation | 1.6821 × |
16821 in other forms
| Form | Value |
|---|---|
| In words | sixteen thousand eight hundred and twenty-one |
| Binary (base 2) | 100000110110101 |
| Octal (base 8) | 40665 |
| Hexadecimal (base 16) | 41B5 |
| Base 3 | 212002000 |
| As time | 16821 seconds = 4 h 40 min 21 s |
Is 16821 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 (16821 ÷ 3 = 5607) | 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 (16821 ÷ 7 = 2403) | 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 (16821 ÷ 9 = 1869) | 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 16821 a prime number?
No. 16821 = × 7 × 89, so it is divisible by 3.
What are the factors of 16821?
1, 3, 7, 9, 21, 27, 63, 89, 189, 267, 623, 801, 1869, 2403, 5607, 16821.
What is 16821 in binary?
100000110110101 (hexadecimal 41B5, octal 40665).
What is the square root of 16821?
About 129.6958, exactly 3√1869.
Is 16821 divisible by 3?
Yes. Its digits add up to 18, a multiple of 3.
What is special about the number 16821?
It is a composite number with 16 divisors.