The number 21655
21655 is a composite number with 8 divisors. Its prime factorisation is 5 × 61 × 71. Divisors (8): 1, 5, 61, 71, 305, 355, 4331, 21655.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 21655: a happy number: repeatedly adding the squares of its digits reaches 1.
- 2
21655 is composite. Its prime factorisation is
- 3
The divisors add up to 26784; without 21655 itself that is 5129, so 21655 is deficient (5129 is less than 21655). Euler's totient φ(21655) = 16800 numbers up to 21655 share no factor with it.
- 4
The digits of 21655 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 43 steps to reach 1.
LaTeX source of the formulas on this page
\[ 21655 = 5 \times 61 \times 71 \]
21655 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 8 |
| Sum of divisors | 26784 |
| Euler totient φ(n) | 16800 |
| Square | 468939025 |
| Cube | 10154874586375 |
| Square root | 147.156379 |
| Digit sum / digital root | 19 / 1 |
| Collatz steps to 1 | 43 |
| Scientific notation | 2.1655 × |
21655 in other forms
| Form | Value |
|---|---|
| In words | twenty-one thousand six hundred and fifty-five |
| Binary (base 2) | 101010010010111 |
| Octal (base 8) | 52227 |
| Hexadecimal (base 16) | 5497 |
| Base 3 | 1002201001 |
| As time | 21655 seconds = 6 h 0 min 55 s |
Is 21655 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 3) | A number is divisible by 4 if the last two digits make a multiple of 4. |
| 5 | Yes (21655 ÷ 5 = 4331) | 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 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 7) | 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 7) | A number is divisible by 11 if the alternating sum of the digits is a multiple of 11. |
| 12 | No (remainder 7) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 21655 a prime number?
No. 21655 = 5 × 61 × 71, so it is divisible by 5.
What are the factors of 21655?
1, 5, 61, 71, 305, 355, 4331, 21655.
What is 21655 in binary?
101010010010111 (hexadecimal 5497, octal 52227).
What is the square root of 21655?
About 147.1564.
Is 21655 divisible by 3?
No. Its digits add up to 19, which is not a multiple of 3.
What is special about the number 21655?
21655 is a happy number: repeatedly adding the squares of its digits reaches 1.