The number 21291
21291 is a composite number with 8 divisors. Its prime factorisation is 3 × 47 × 151. Divisors (8): 1, 3, 47, 141, 151, 453, 7097, 21291.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 21291: a happy number: repeatedly adding the squares of its digits reaches 1.
- 2
21291 is composite. Its prime factorisation is
- 3
The divisors add up to 29184; without 21291 itself that is 7893, so 21291 is deficient (7893 is less than 21291). Euler's totient φ(21291) = 13800 numbers up to 21291 share no factor with it.
- 4
The digits of 21291 add up to 15, and repeating that until one digit is left gives the digital root 6. The Collatz sequence (halve if even, else 3n+1) takes 193 steps to reach 1.
LaTeX source of the formulas on this page
\[ 21291 = 3 \times 47 \times 151 \]
21291 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 8 |
| Sum of divisors | 29184 |
| Euler totient φ(n) | 13800 |
| Square | 453306681 |
| Cube | 9651352545171 |
| Square root | 145.914358 |
| Digit sum / digital root | 15 / 6 |
| Collatz steps to 1 | 193 |
| Scientific notation | 2.1291 × |
21291 in other forms
| Form | Value |
|---|---|
| In words | twenty-one thousand two hundred and ninety-one |
| Binary (base 2) | 101001100101011 |
| Octal (base 8) | 51453 |
| Hexadecimal (base 16) | 532B |
| Base 3 | 1002012120 |
| As time | 21291 seconds = 5 h 54 min 51 s |
Is 21291 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 | Yes (21291 ÷ 3 = 7097) | A number is divisible by 3 if the digits add up to a multiple of 3. |
| 4 | No (remainder 3) | 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 3) | 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 3) | A number is divisible by 8 if the last three digits make a multiple of 8. |
| 9 | No (remainder 6) | 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 3) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 21291 a prime number?
No. 21291 = 3 × 47 × 151, so it is divisible by 3.
What are the factors of 21291?
1, 3, 47, 141, 151, 453, 7097, 21291.
What is 21291 in binary?
101001100101011 (hexadecimal 532B, octal 51453).
What is the square root of 21291?
About 145.9144.
Is 21291 divisible by 3?
Yes. Its digits add up to 15, a multiple of 3.
What is special about the number 21291?
21291 is a happy number: repeatedly adding the squares of its digits reaches 1.