The number 12821
12821 is a palindromic prime: it reads the same backwards and is prime, a twin prime (12821 and 12823 are both prime) and the 1528th prime number. Its only divisors are 1 and 12821.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 12821: a palindromic prime: it reads the same backwards and is prime; a twin prime (12821 and 12823 are both prime); the 1528th prime number; a palindrome: it reads 12821 backwards too.
- 2
12821 is prime, so its only factors are 1 and 12821. It is the 1528th prime; the next prime is 12823 and the one before is 12809.
- 3
The divisors add up to 12822; without 12821 itself that is 1, so 12821 is deficient (1 is less than 12821). Euler's totient φ(12821) = 12820 numbers up to 12821 share no factor with it.
- 4
The digits of 12821 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 63 steps to reach 1.
12821 at a glance
| Property | Value |
|---|---|
| Type | prime |
| Number of divisors | 2 |
| Sum of divisors | 12822 |
| Euler totient φ(n) | 12820 |
| Square | 164378041 |
| Cube | 2107490863661 |
| Square root | 113.229855 |
| Digit sum / digital root | 14 / 5 |
| Collatz steps to 1 | 63 |
| Scientific notation | 1.2821 × |
12821 in other forms
| Form | Value |
|---|---|
| In words | twelve thousand eight hundred and twenty-one |
| Binary (base 2) | 11001000010101 |
| Octal (base 8) | 31025 |
| Hexadecimal (base 16) | 3215 |
| Base 3 | 122120212 |
| As time | 12821 seconds = 3 h 33 min 41 s |
Is 12821 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 4) | 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 6) | 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 12821 a prime number?
Yes. 12821 is divisible only by 1 and itself.
What are the factors of 12821?
1, 12821.
What is 12821 in binary?
11001000010101 (hexadecimal 3215, octal 31025).
What is the square root of 12821?
About 113.2299.
Is 12821 divisible by 3?
No. Its digits add up to 14, which is not a multiple of 3.
What is special about the number 12821?
12821 is a palindromic prime: it reads the same backwards and is prime; a twin prime (12821 and 12823 are both prime); the 1528th prime number; a palindrome: it reads 12821 backwards too.