The number 12721
12721 is a palindromic prime: it reads the same backwards and is prime, the 1519th prime number and a palindrome: it reads 12721 backwards too. Its only divisors are 1 and 12721.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 12721: a palindromic prime: it reads the same backwards and is prime; the 1519th prime number; a palindrome: it reads 12721 backwards too.
- 2
12721 is prime, so its only factors are 1 and 12721. It is the 1519th prime; the next prime is 12739 and the one before is 12713.
- 3
The divisors add up to 12722; without 12721 itself that is 1, so 12721 is deficient (1 is less than 12721). Euler's totient φ(12721) = 12720 numbers up to 12721 share no factor with it.
- 4
The digits of 12721 add up to 13, and repeating that until one digit is left gives the digital root 4. The Collatz sequence (halve if even, else 3n+1) takes 107 steps to reach 1.
12721 at a glance
| Property | Value |
|---|---|
| Type | prime |
| Number of divisors | 2 |
| Sum of divisors | 12722 |
| Euler totient φ(n) | 12720 |
| Square | 161823841 |
| Cube | 2058561081361 |
| Square root | 112.787411 |
| Digit sum / digital root | 13 / 4 |
| Collatz steps to 1 | 107 |
| Scientific notation | 1.2721 × |
12721 in other forms
| Form | Value |
|---|---|
| In words | twelve thousand seven hundred and twenty-one |
| Binary (base 2) | 11000110110001 |
| Octal (base 8) | 30661 |
| Hexadecimal (base 16) | 31B1 |
| Base 3 | 122110011 |
| As time | 12721 seconds = 3 h 32 min 1 s |
Is 12721 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 1) | 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 1) | 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 1) | A number is divisible by 8 if the last three digits make a multiple of 8. |
| 9 | No (remainder 4) | 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 5) | A number is divisible by 11 if the alternating sum of the digits is a multiple of 11. |
| 12 | No (remainder 1) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 12721 a prime number?
Yes. 12721 is divisible only by 1 and itself.
What are the factors of 12721?
1, 12721.
What is 12721 in binary?
11000110110001 (hexadecimal 31B1, octal 30661).
What is the square root of 12721?
About 112.7874.
Is 12721 divisible by 3?
No. Its digits add up to 13, which is not a multiple of 3.
What is special about the number 12721?
12721 is a palindromic prime: it reads the same backwards and is prime; the 1519th prime number; a palindrome: it reads 12721 backwards too.