The number 21181
21181 is a composite number with 4 divisors. Its prime factorisation is 59 × 359. Divisors (4): 1, 59, 359, 21181.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 21181: a semiprime: 59 × 359, the product of two primes.
- 2
21181 is composite. Its prime factorisation is
- 3
The divisors add up to 21600; without 21181 itself that is 419, so 21181 is deficient (419 is less than 21181). Euler's totient φ(21181) = 20764 numbers up to 21181 share no factor with it.
- 4
The digits of 21181 add up to 13, and repeating that until one digit is left gives the digital root 4. The Collatz sequence (halve if even, else 3n+1) takes 149 steps to reach 1.
LaTeX source of the formulas on this page
\[ 21181 = 59 \times 359 \]
21181 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 4 |
| Sum of divisors | 21600 |
| Euler totient φ(n) | 20764 |
| Square | 448634761 |
| Cube | 9502532872741 |
| Square root | 145.536937 |
| Digit sum / digital root | 13 / 4 |
| Collatz steps to 1 | 149 |
| Scientific notation | 2.1181 × |
21181 in other forms
| Form | Value |
|---|---|
| In words | twenty-one thousand one hundred and eighty-one |
| Binary (base 2) | 101001010111101 |
| Octal (base 8) | 51275 |
| Hexadecimal (base 16) | 52BD |
| Base 3 | 1002001111 |
| As time | 21181 seconds = 5 h 53 min 1 s |
Is 21181 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 | No (remainder 1) | 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 6) | 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 4) | 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 1) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 21181 a prime number?
No. 21181 = 59 × 359, so it is divisible by 59.
What are the factors of 21181?
1, 59, 359, 21181.
What is 21181 in binary?
101001010111101 (hexadecimal 52BD, octal 51275).
What is the square root of 21181?
About 145.5369.
Is 21181 divisible by 3?
No. Its digits add up to 13, which is not a multiple of 3.
What is special about the number 21181?
21181 is a semiprime: 59 × 359, the product of two primes.