The number 21931
21931 is a composite number with 8 divisors. Its prime factorisation is 7 × 13 × 241. Divisors (8): 1, 7, 13, 91, 241, 1687, 3133, 21931.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
21931 has no famous special property in the usual lists (prime, square, cube, triangular, Fibonacci, palindrome, perfect), but it is still a composite number.
- 2
21931 is composite. Its prime factorisation is
- 3
The divisors add up to 27104; without 21931 itself that is 5173, so 21931 is deficient (5173 is less than 21931). Euler's totient φ(21931) = 17280 numbers up to 21931 share no factor with it.
- 4
The digits of 21931 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 100 steps to reach 1.
LaTeX source of the formulas on this page
\[ 21931 = 7 \times 13 \times 241 \]
21931 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 8 |
| Sum of divisors | 27104 |
| Euler totient φ(n) | 17280 |
| Square | 480968761 |
| Cube | 10548125897491 |
| Square root | 148.091188 |
| Digit sum / digital root | 16 / 7 |
| Collatz steps to 1 | 100 |
| Scientific notation | 2.1931 × |
21931 in other forms
| Form | Value |
|---|---|
| In words | twenty-one thousand nine hundred and thirty-one |
| Binary (base 2) | 101010110101011 |
| Octal (base 8) | 52653 |
| Hexadecimal (base 16) | 55AB |
| Base 3 | 1010002021 |
| As time | 21931 seconds = 6 h 5 min 31 s |
Is 21931 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 (21931 ÷ 7 = 3133) | 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 1) | A number is divisible by 10 if the last digit is 0. |
| 11 | No (remainder 8) | 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 21931 a prime number?
No. 21931 = 7 × 13 × 241, so it is divisible by 7.
What are the factors of 21931?
1, 7, 13, 91, 241, 1687, 3133, 21931.
What is 21931 in binary?
101010110101011 (hexadecimal 55AB, octal 52653).
What is the square root of 21931?
About 148.0912.
Is 21931 divisible by 3?
No. Its digits add up to 16, which is not a multiple of 3.
What is special about the number 21931?
It is a composite number with 8 divisors.