The number 21565
21565 is a composite number with 8 divisors. Its prime factorisation is 5 × 19 × 227. Divisors (8): 1, 5, 19, 95, 227, 1135, 4313, 21565.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 21565: a happy number: repeatedly adding the squares of its digits reaches 1; a Harshad number: divisible by its digit sum 19.
- 2
21565 is composite. Its prime factorisation is
- 3
The divisors add up to 27360; without 21565 itself that is 5795, so 21565 is deficient (5795 is less than 21565). Euler's totient φ(21565) = 16272 numbers up to 21565 share no factor with it.
- 4
The digits of 21565 add up to 19, and repeating that until one digit is left gives the digital root 1. The Collatz sequence (halve if even, else 3n+1) takes 30 steps to reach 1.
LaTeX source of the formulas on this page
\[ 21565 = 5 \times 19 \times 227 \]
21565 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 8 |
| Sum of divisors | 27360 |
| Euler totient φ(n) | 16272 |
| Square | 465049225 |
| Cube | 10028786537125 |
| Square root | 146.850264 |
| Digit sum / digital root | 19 / 1 |
| Collatz steps to 1 | 30 |
| Scientific notation | 2.1565 × |
21565 in other forms
| Form | Value |
|---|---|
| In words | twenty-one thousand five hundred and sixty-five |
| Binary (base 2) | 101010000111101 |
| Octal (base 8) | 52075 |
| Hexadecimal (base 16) | 543D |
| Base 3 | 1002120201 |
| As time | 21565 seconds = 5 h 59 min 25 s |
Is 21565 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 | Yes (21565 ÷ 5 = 4313) | 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 5) | A number is divisible by 8 if the last three digits make a multiple of 8. |
| 9 | No (remainder 1) | 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 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 21565 a prime number?
No. 21565 = 5 × 19 × 227, so it is divisible by 5.
What are the factors of 21565?
1, 5, 19, 95, 227, 1135, 4313, 21565.
What is 21565 in binary?
101010000111101 (hexadecimal 543D, octal 52075).
What is the square root of 21565?
About 146.8503.
Is 21565 divisible by 3?
No. Its digits add up to 19, which is not a multiple of 3.
What is special about the number 21565?
21565 is a happy number: repeatedly adding the squares of its digits reaches 1; a Harshad number: divisible by its digit sum 19.