The number 42821
42821 is the 4477th prime number. Its only divisors are 1 and 42821.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 42821: the 4477th prime number.
- 2
42821 is prime, so its only factors are 1 and 42821. It is the 4477th prime; the next prime is 42829 and the one before is 42797.
- 3
The divisors add up to 42822; without 42821 itself that is 1, so 42821 is deficient (1 is less than 42821). Euler's totient φ(42821) = 42820 numbers up to 42821 share no factor with it.
- 4
The digits of 42821 add up to 17, and repeating that until one digit is left gives the digital root 8. The Collatz sequence (halve if even, else 3n+1) takes 49 steps to reach 1.
42821 at a glance
| Property | Value |
|---|---|
| Type | prime |
| Number of divisors | 2 |
| Sum of divisors | 42822 |
| Euler totient φ(n) | 42820 |
| Square | 1833638041 |
| Cube | 78518214553661 |
| Square root | 206.932356 |
| Digit sum / digital root | 17 / 8 |
| Collatz steps to 1 | 49 |
| Scientific notation | 4.2821 × |
42821 in other forms
| Form | Value |
|---|---|
| In words | forty-two thousand eight hundred and twenty-one |
| Binary (base 2) | 1010011101000101 |
| Octal (base 8) | 123505 |
| Hexadecimal (base 16) | A745 |
| Base 3 | 2011201222 |
| As time | 42821 seconds = 11 h 53 min 41 s |
Is 42821 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 2) | 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 8) | 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 42821 a prime number?
Yes. 42821 is divisible only by 1 and itself.
What are the factors of 42821?
1, 42821.
What is 42821 in binary?
1010011101000101 (hexadecimal A745, octal 123505).
What is the square root of 42821?
About 206.9324.
Is 42821 divisible by 3?
No. Its digits add up to 17, which is not a multiple of 3.
What is special about the number 42821?
42821 is the 4477th prime number.