The number 21191
21191 is a twin prime (21191 and 21193 are both prime) and the 2383rd prime number. Its only divisors are 1 and 21191.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 21191: a twin prime (21191 and 21193 are both prime); the 2383rd prime number.
- 2
21191 is prime, so its only factors are 1 and 21191. It is the 2383rd prime; the next prime is 21193 and the one before is 21187.
- 3
The divisors add up to 21192; without 21191 itself that is 1, so 21191 is deficient (1 is less than 21191). Euler's totient φ(21191) = 21190 numbers up to 21191 share no factor with it.
- 4
The digits of 21191 add up to 14, and repeating that until one digit is left gives the digital root 5. The Collatz sequence (halve if even, else 3n+1) takes 56 steps to reach 1.
21191 at a glance
| Property | Value |
|---|---|
| Type | prime |
| Number of divisors | 2 |
| Sum of divisors | 21192 |
| Euler totient φ(n) | 21190 |
| Square | 449058481 |
| Cube | 9515998270871 |
| Square root | 145.571288 |
| Digit sum / digital root | 14 / 5 |
| Collatz steps to 1 | 56 |
| Scientific notation | 2.1191 × |
21191 in other forms
| Form | Value |
|---|---|
| In words | twenty-one thousand one hundred and ninety-one |
| Binary (base 2) | 101001011000111 |
| Octal (base 8) | 51307 |
| Hexadecimal (base 16) | 52C7 |
| Base 3 | 1002001212 |
| As time | 21191 seconds = 5 h 53 min 11 s |
Is 21191 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 2) | 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 5) | A number is divisible by 6 if it is divisible by both 2 and 3. |
| 7 | No (remainder 2) | 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 5) | 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 5) | A number is divisible by 11 if the alternating sum of the digits is a multiple of 11. |
| 12 | No (remainder 11) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 21191 a prime number?
Yes. 21191 is divisible only by 1 and itself.
What are the factors of 21191?
1, 21191.
What is 21191 in binary?
101001011000111 (hexadecimal 52C7, octal 51307).
What is the square root of 21191?
About 145.5713.
Is 21191 divisible by 3?
No. Its digits add up to 14, which is not a multiple of 3.
What is special about the number 21191?
21191 is a twin prime (21191 and 21193 are both prime); the 2383rd prime number.