The number 21355
21355 is a composite number with 4 divisors. Its prime factorisation is 5 × 4271. Divisors (4): 1, 5, 4271, 21355.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 21355: a semiprime: 5 × 4271, the product of two primes.
- 2
21355 is composite. Its prime factorisation is
- 3
The divisors add up to 25632; without 21355 itself that is 4277, so 21355 is deficient (4277 is less than 21355). Euler's totient φ(21355) = 17080 numbers up to 21355 share no factor with it.
- 4
The digits of 21355 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 48 steps to reach 1.
LaTeX source of the formulas on this page
\[ 21355 = 5 \times 4271 \]
21355 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 4 |
| Sum of divisors | 25632 |
| Euler totient φ(n) | 17080 |
| Square | 456036025 |
| Cube | 9738649313875 |
| Square root | 146.133501 |
| Digit sum / digital root | 16 / 7 |
| Collatz steps to 1 | 48 |
| Scientific notation | 2.1355 × |
21355 in other forms
| Form | Value |
|---|---|
| In words | twenty-one thousand three hundred and fifty-five |
| Binary (base 2) | 101001101101011 |
| Octal (base 8) | 51553 |
| Hexadecimal (base 16) | 536B |
| Base 3 | 1002021221 |
| As time | 21355 seconds = 5 h 55 min 55 s |
Is 21355 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 (21355 ÷ 5 = 4271) | 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 3) | 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 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 7) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 21355 a prime number?
No. 21355 = 5 × 4271, so it is divisible by 5.
What are the factors of 21355?
1, 5, 4271, 21355.
What is 21355 in binary?
101001101101011 (hexadecimal 536B, octal 51553).
What is the square root of 21355?
About 146.1335.
Is 21355 divisible by 3?
No. Its digits add up to 16, which is not a multiple of 3.
What is special about the number 21355?
21355 is a semiprime: 5 × 4271, the product of two primes.