The number 21465
21465 is a composite number with 20 divisors. Its prime factorisation is × 5 × 53. Divisors (20): 1, 3, 5, 9, 15, 27, 45, 53, 81, 135, 159, 265, 405, 477, 795, 1431 … 21465.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 21465: a happy number: repeatedly adding the squares of its digits reaches 1.
- 2
21465 is composite. Its prime factorisation is
- 3
The divisors add up to 39204; without 21465 itself that is 17739, so 21465 is deficient (17739 is less than 21465). Euler's totient φ(21465) = 11232 numbers up to 21465 share no factor with it.
- 4
The digits of 21465 add up to 18, and repeating that until one digit is left gives the digital root 9. The Collatz sequence (halve if even, else 3n+1) takes 74 steps to reach 1.
LaTeX source of the formulas on this page
\[ 21465 = 3^{4} \times 5 \times 53 \]21465 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 20 |
| Sum of divisors | 39204 |
| Euler totient φ(n) | 11232 |
| Square | 460746225 |
| Cube | 9889917719625 |
| Square root | 146.509385 (= 9√265) |
| Digit sum / digital root | 18 / 9 |
| Collatz steps to 1 | 74 |
| Scientific notation | 2.1465 × |
21465 in other forms
| Form | Value |
|---|---|
| In words | twenty-one thousand four hundred and sixty-five |
| Binary (base 2) | 101001111011001 |
| Octal (base 8) | 51731 |
| Hexadecimal (base 16) | 53D9 |
| Base 3 | 1002110000 |
| As time | 21465 seconds = 5 h 57 min 45 s |
Is 21465 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 (21465 ÷ 3 = 7155) | 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 | Yes (21465 ÷ 5 = 4293) | 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 3) | 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 | Yes (21465 ÷ 9 = 2385) | A number is divisible by 9 if the digits add up to a multiple of 9. |
| 10 | No (remainder 5) | A number is divisible by 10 if the last digit is 0. |
| 11 | No (remainder 4) | A number is divisible by 11 if the alternating sum of the digits is a multiple of 11. |
| 12 | No (remainder 9) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 21465 a prime number?
No. 21465 = × 5 × 53, so it is divisible by 3.
What are the factors of 21465?
1, 3, 5, 9, 15, 27, 45, 53, 81, 135, 159, 265, 405, 477, 795, 1431, 2385, 4293, 7155, 21465.
What is 21465 in binary?
101001111011001 (hexadecimal 53D9, octal 51731).
What is the square root of 21465?
About 146.5094, exactly 9√265.
Is 21465 divisible by 3?
Yes. Its digits add up to 18, a multiple of 3.
What is special about the number 21465?
21465 is a happy number: repeatedly adding the squares of its digits reaches 1.