The number 31821
31821 is a composite number with 4 divisors. Its prime factorisation is 3 × 10607. Divisors (4): 1, 3, 10607, 31821.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 31821: a happy number: repeatedly adding the squares of its digits reaches 1; a semiprime: 3 × 10607, the product of two primes.
- 2
31821 is composite. Its prime factorisation is
- 3
The divisors add up to 42432; without 31821 itself that is 10611, so 31821 is deficient (10611 is less than 31821). Euler's totient φ(31821) = 21212 numbers up to 31821 share no factor with it.
- 4
The digits of 31821 add up to 15, and repeating that until one digit is left gives the digital root 6. The Collatz sequence (halve if even, else 3n+1) takes 147 steps to reach 1.
LaTeX source of the formulas on this page
\[ 31821 = 3 \times 10607 \]
31821 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 4 |
| Sum of divisors | 42432 |
| Euler totient φ(n) | 21212 |
| Square | 1012576041 |
| Cube | 32221182200661 |
| Square root | 178.384416 |
| Digit sum / digital root | 15 / 6 |
| Collatz steps to 1 | 147 |
| Scientific notation | 3.1821 × |
31821 in other forms
| Form | Value |
|---|---|
| In words | thirty-one thousand eight hundred and twenty-one |
| Binary (base 2) | 111110001001101 |
| Octal (base 8) | 76115 |
| Hexadecimal (base 16) | 7C4D |
| Base 3 | 1121122120 |
| As time | 31821 seconds = 8 h 50 min 21 s |
Is 31821 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 (31821 ÷ 3 = 10607) | 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 6) | 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 9) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 31821 a prime number?
No. 31821 = 3 × 10607, so it is divisible by 3.
What are the factors of 31821?
1, 3, 10607, 31821.
What is 31821 in binary?
111110001001101 (hexadecimal 7C4D, octal 76115).
What is the square root of 31821?
About 178.3844.
Is 31821 divisible by 3?
Yes. Its digits add up to 15, a multiple of 3.
What is special about the number 31821?
31821 is a happy number: repeatedly adding the squares of its digits reaches 1; a semiprime: 3 × 10607, the product of two primes.