The number 3821
3821 is a twin prime (3821 and 3823 are both prime) and the 530th prime number. Its only divisors are 1 and 3821.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 3821: a twin prime (3821 and 3823 are both prime); the 530th prime number.
- 2
3821 is prime, so its only factors are 1 and 3821. It is the 530th prime; the next prime is 3823 and the one before is 3803.
- 3
The divisors add up to 3822; without 3821 itself that is 1, so 3821 is deficient (1 is less than 3821). Euler's totient φ(3821) = 3820 numbers up to 3821 share no factor with it.
- 4
The digits of 3821 add up to 14, and repeating that until one digit is left gives the digital root 5. The Collatz sequence (halve if even, else 3n+1) takes 30 steps to reach 1.
3821 at a glance
| Property | Value |
|---|---|
| Type | prime |
| Number of divisors | 2 |
| Sum of divisors | 3822 |
| Euler totient φ(n) | 3820 |
| Square | 14600041 |
| Cube | 55786756661 |
| Square root | 61.814238 |
| Digit sum / digital root | 14 / 5 |
| Collatz steps to 1 | 30 |
| Scientific notation | 3.821 × |
3821 in other forms
| Form | Value |
|---|---|
| In words | three thousand eight hundred and twenty-one |
| Roman numerals | MMMDCCCXXI |
| Binary (base 2) | 111011101101 |
| Octal (base 8) | 7355 |
| Hexadecimal (base 16) | EED |
| Base 3 | 12020112 |
| As time | 3821 seconds = 1 h 3 min 41 s |
Is 3821 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 | 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 5) | 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 4) | 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 3821 a prime number?
Yes. 3821 is divisible only by 1 and itself.
What are the factors of 3821?
1, 3821.
What is 3821 in binary?
111011101101 (hexadecimal EED, octal 7355).
What is the square root of 3821?
About 61.8142.
What is 3821 in Roman numerals?
MMMDCCCXXI.
Is 3821 divisible by 3?
No. Its digits add up to 14, which is not a multiple of 3.
What is special about the number 3821?
3821 is a twin prime (3821 and 3823 are both prime); the 530th prime number.