The number 9821
9821 is a composite number with 8 divisors. Its prime factorisation is 7 × 23 × 61. Divisors (8): 1, 7, 23, 61, 161, 427, 1403, 9821.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
9821 has no famous special property in the usual lists (prime, square, cube, triangular, Fibonacci, palindrome, perfect), but it is still a composite number.
- 2
9821 is composite. Its prime factorisation is
- 3
The divisors add up to 11904; without 9821 itself that is 2083, so 9821 is deficient (2083 is less than 9821). Euler's totient φ(9821) = 7920 numbers up to 9821 share no factor with it.
- 4
The digits of 9821 add up to 20, and repeating that until one digit is left gives the digital root 2. The Collatz sequence (halve if even, else 3n+1) takes 135 steps to reach 1.
LaTeX source of the formulas on this page
\[ 9821 = 7 \times 23 \times 61 \]
9821 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 8 |
| Sum of divisors | 11904 |
| Euler totient φ(n) | 7920 |
| Square | 96452041 |
| Cube | 947255494661 |
| Square root | 99.100959 |
| Digit sum / digital root | 20 / 2 |
| Collatz steps to 1 | 135 |
| Scientific notation | 9.821 × |
9821 in other forms
| Form | Value |
|---|---|
| In words | nine thousand eight hundred and twenty-one |
| Binary (base 2) | 10011001011101 |
| Octal (base 8) | 23135 |
| Hexadecimal (base 16) | 265D |
| Base 3 | 111110202 |
| As time | 9821 seconds = 2 h 43 min 41 s |
Is 9821 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 2) | 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 5) | A number is divisible by 6 if it is divisible by both 2 and 3. |
| 7 | Yes (9821 ÷ 7 = 1403) | 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 2) | 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 9) | A number is divisible by 11 if the alternating sum of the digits is a multiple of 11. |
| 12 | No (remainder 5) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 9821 a prime number?
No. 9821 = 7 × 23 × 61, so it is divisible by 7.
What are the factors of 9821?
1, 7, 23, 61, 161, 427, 1403, 9821.
What is 9821 in binary?
10011001011101 (hexadecimal 265D, octal 23135).
What is the square root of 9821?
About 99.1010.
Is 9821 divisible by 3?
No. Its digits add up to 20, which is not a multiple of 3.
What is special about the number 9821?
It is a composite number with 8 divisors.