The number 21091
21091 is a composite number with 8 divisors. Its prime factorisation is 7 × 23 × 131. Divisors (8): 1, 7, 23, 131, 161, 917, 3013, 21091.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
21091 has no famous special property in the usual lists (prime, square, cube, triangular, Fibonacci, palindrome, perfect), but it is still a composite number.
- 2
21091 is composite. Its prime factorisation is
- 3
The divisors add up to 25344; without 21091 itself that is 4253, so 21091 is deficient (4253 is less than 21091). Euler's totient φ(21091) = 17160 numbers up to 21091 share no factor with it.
- 4
The digits of 21091 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
\[ 21091 = 7 \times 23 \times 131 \]
21091 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 8 |
| Sum of divisors | 25344 |
| Euler totient φ(n) | 17160 |
| Square | 444830281 |
| Cube | 9381915456571 |
| Square root | 145.227408 |
| Digit sum / digital root | 13 / 4 |
| Collatz steps to 1 | 149 |
| Scientific notation | 2.1091 × |
21091 in other forms
| Form | Value |
|---|---|
| In words | twenty-one thousand and ninety-one |
| Binary (base 2) | 101001001100011 |
| Octal (base 8) | 51143 |
| Hexadecimal (base 16) | 5263 |
| Base 3 | 1001221011 |
| As time | 21091 seconds = 5 h 51 min 31 s |
Is 21091 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 | 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 | Yes (21091 ÷ 7 = 3013) | 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 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 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 21091 a prime number?
No. 21091 = 7 × 23 × 131, so it is divisible by 7.
What are the factors of 21091?
1, 7, 23, 131, 161, 917, 3013, 21091.
What is 21091 in binary?
101001001100011 (hexadecimal 5263, octal 51143).
What is the square root of 21091?
About 145.2274.
Is 21091 divisible by 3?
No. Its digits add up to 13, which is not a multiple of 3.
What is special about the number 21091?
It is a composite number with 8 divisors.