The number 11981
11981 is the 1437th prime number. Its only divisors are 1 and 11981.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 11981: the 1437th prime number.
- 2
11981 is prime, so its only factors are 1 and 11981. It is the 1437th prime; the next prime is 11987 and the one before is 11971.
- 3
The divisors add up to 11982; without 11981 itself that is 1, so 11981 is deficient (1 is less than 11981). Euler's totient φ(11981) = 11980 numbers up to 11981 share no factor with it.
- 4
The digits of 11981 add up to 20, and repeating that until one digit is left gives the digital root 2. The Collatz sequence (halve if even, else 3n+1) takes 50 steps to reach 1.
11981 at a glance
| Property | Value |
|---|---|
| Type | prime |
| Number of divisors | 2 |
| Sum of divisors | 11982 |
| Euler totient φ(n) | 11980 |
| Square | 143544361 |
| Cube | 1719804989141 |
| Square root | 109.457754 |
| Digit sum / digital root | 20 / 2 |
| Collatz steps to 1 | 50 |
| Scientific notation | 1.1981 × |
11981 in other forms
| Form | Value |
|---|---|
| In words | eleven thousand nine hundred and eighty-one |
| Binary (base 2) | 10111011001101 |
| Octal (base 8) | 27315 |
| Hexadecimal (base 16) | 2ECD |
| Base 3 | 121102202 |
| As time | 11981 seconds = 3 h 19 min 41 s |
Is 11981 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 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 5) | A number is divisible by 6 if it is divisible by both 2 and 3. |
| 7 | No (remainder 4) | 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 2) | 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 2) | A number is divisible by 11 if the alternating sum of the digits is a multiple of 11. |
| 12 | No (remainder 5) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 11981 a prime number?
Yes. 11981 is divisible only by 1 and itself.
What are the factors of 11981?
1, 11981.
What is 11981 in binary?
10111011001101 (hexadecimal 2ECD, octal 27315).
What is the square root of 11981?
About 109.4578.
Is 11981 divisible by 3?
No. Its digits add up to 20, which is not a multiple of 3.
What is special about the number 11981?
11981 is the 1437th prime number.