The number 87991
87991 is the 8543rd prime number. Its only divisors are 1 and 87991.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 87991: the 8543rd prime number.
- 2
87991 is prime, so its only factors are 1 and 87991. It is the 8543rd prime; the next prime is 88001 and the one before is 87977.
- 3
The divisors add up to 87992; without 87991 itself that is 1, so 87991 is deficient (1 is less than 87991). Euler's totient φ(87991) = 87990 numbers up to 87991 share no factor with it.
- 4
The digits of 87991 add up to 34, and repeating that until one digit is left gives the digital root 7. The Collatz sequence (halve if even, else 3n+1) takes 120 steps to reach 1.
87991 at a glance
| Property | Value |
|---|---|
| Type | prime |
| Number of divisors | 2 |
| Sum of divisors | 87992 |
| Euler totient φ(n) | 87990 |
| Square | 7742416081 |
| Cube | 681262933383271 |
| Square root | 296.632770 |
| Digit sum / digital root | 34 / 7 |
| Collatz steps to 1 | 120 |
| Scientific notation | 8.7991 × |
87991 in other forms
| Form | Value |
|---|---|
| In words | eighty-seven thousand nine hundred and ninety-one |
| Binary (base 2) | 10101011110110111 |
| Octal (base 8) | 253667 |
| Hexadecimal (base 16) | 157B7 |
| Base 3 | 11110200221 |
| As time | 87991 seconds = 24 h 26 min 31 s |
Is 87991 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 | No (remainder 1) | 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 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 2) | 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 87991 a prime number?
Yes. 87991 is divisible only by 1 and itself.
What are the factors of 87991?
1, 87991.
What is 87991 in binary?
10101011110110111 (hexadecimal 157B7, octal 253667).
What is the square root of 87991?
About 296.6328.
Is 87991 divisible by 3?
No. Its digits add up to 34, which is not a multiple of 3.
What is special about the number 87991?
87991 is the 8543rd prime number.