The number 21481
21481 is the 2408th prime number. Its only divisors are 1 and 21481.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 21481: the 2408th prime number; a happy number: repeatedly adding the squares of its digits reaches 1.
- 2
21481 is prime, so its only factors are 1 and 21481. It is the 2408th prime; the next prime is 21487 and the one before is 21467.
- 3
The divisors add up to 21482; without 21481 itself that is 1, so 21481 is deficient (1 is less than 21481). Euler's totient φ(21481) = 21480 numbers up to 21481 share no factor with it.
- 4
The digits of 21481 add up to 16, and repeating that until one digit is left gives the digital root 7. The Collatz sequence (halve if even, else 3n+1) takes 149 steps to reach 1.
21481 at a glance
| Property | Value |
|---|---|
| Type | prime |
| Number of divisors | 2 |
| Sum of divisors | 21482 |
| Euler totient φ(n) | 21480 |
| Square | 461433361 |
| Cube | 9912050027641 |
| Square root | 146.563979 |
| Digit sum / digital root | 16 / 7 |
| Collatz steps to 1 | 149 |
| Scientific notation | 2.1481 × |
21481 in other forms
| Form | Value |
|---|---|
| In words | twenty-one thousand four hundred and eighty-one |
| Binary (base 2) | 101001111101001 |
| Octal (base 8) | 51751 |
| Hexadecimal (base 16) | 53E9 |
| Base 3 | 1002110121 |
| As time | 21481 seconds = 5 h 58 min 1 s |
Is 21481 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 5) | 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 7) | 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 1) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 21481 a prime number?
Yes. 21481 is divisible only by 1 and itself.
What are the factors of 21481?
1, 21481.
What is 21481 in binary?
101001111101001 (hexadecimal 53E9, octal 51751).
What is the square root of 21481?
About 146.5640.
Is 21481 divisible by 3?
No. Its digits add up to 16, which is not a multiple of 3.
What is special about the number 21481?
21481 is the 2408th prime number; a happy number: repeatedly adding the squares of its digits reaches 1.