The number 10821
10821 is a composite number with 4 divisors. Its prime factorisation is 3 × 3607. Divisors (4): 1, 3, 3607, 10821.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 10821: a happy number: repeatedly adding the squares of its digits reaches 1; a semiprime: 3 × 3607, the product of two primes.
- 2
10821 is composite. Its prime factorisation is
- 3
The divisors add up to 14432; without 10821 itself that is 3611, so 10821 is deficient (3611 is less than 10821). Euler's totient φ(10821) = 7212 numbers up to 10821 share no factor with it.
- 4
The digits of 10821 add up to 12, and repeating that until one digit is left gives the digital root 3. The Collatz sequence (halve if even, else 3n+1) takes 42 steps to reach 1.
LaTeX source of the formulas on this page
\[ 10821 = 3 \times 3607 \]
10821 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 4 |
| Sum of divisors | 14432 |
| Euler totient φ(n) | 7212 |
| Square | 117094041 |
| Cube | 1267074617661 |
| Square root | 104.024036 |
| Digit sum / digital root | 12 / 3 |
| Collatz steps to 1 | 42 |
| Scientific notation | 1.0821 × |
10821 in other forms
| Form | Value |
|---|---|
| In words | ten thousand eight hundred and twenty-one |
| Binary (base 2) | 10101001000101 |
| Octal (base 8) | 25105 |
| Hexadecimal (base 16) | 2A45 |
| Base 3 | 112211210 |
| As time | 10821 seconds = 3 h 0 min 21 s |
Is 10821 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 (10821 ÷ 3 = 3607) | 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 6) | 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 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 8) | 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 10821 a prime number?
No. 10821 = 3 × 3607, so it is divisible by 3.
What are the factors of 10821?
1, 3, 3607, 10821.
What is 10821 in binary?
10101001000101 (hexadecimal 2A45, octal 25105).
What is the square root of 10821?
About 104.0240.
Is 10821 divisible by 3?
Yes. Its digits add up to 12, a multiple of 3.
What is special about the number 10821?
10821 is a happy number: repeatedly adding the squares of its digits reaches 1; a semiprime: 3 × 3607, the product of two primes.