The number 87721
87721 is a twin prime (87719 and 87721 are both prime) and the 8520th prime number. Its only divisors are 1 and 87721.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 87721: a twin prime (87719 and 87721 are both prime); the 8520th prime number; a happy number: repeatedly adding the squares of its digits reaches 1.
- 2
87721 is prime, so its only factors are 1 and 87721. It is the 8520th prime; the next prime is 87739 and the one before is 87719.
- 3
The divisors add up to 87722; without 87721 itself that is 1, so 87721 is deficient (1 is less than 87721). Euler's totient φ(87721) = 87720 numbers up to 87721 share no factor with it.
- 4
The digits of 87721 add up to 25, and repeating that until one digit is left gives the digital root 7. The Collatz sequence (halve if even, else 3n+1) takes 164 steps to reach 1.
87721 at a glance
| Property | Value |
|---|---|
| Type | prime |
| Number of divisors | 2 |
| Sum of divisors | 87722 |
| Euler totient φ(n) | 87720 |
| Square | 7694973841 |
| Cube | 675010800306361 |
| Square root | 296.177312 |
| Digit sum / digital root | 25 / 7 |
| Collatz steps to 1 | 164 |
| Scientific notation | 8.7721 × |
87721 in other forms
| Form | Value |
|---|---|
| In words | eighty-seven thousand seven hundred and twenty-one |
| Binary (base 2) | 10101011010101001 |
| Octal (base 8) | 253251 |
| Hexadecimal (base 16) | 156A9 |
| Base 3 | 11110022221 |
| As time | 87721 seconds = 24 h 22 min 1 s |
Is 87721 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 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 1) | 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 1) | 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 7) | A number is divisible by 11 if the alternating sum of the digits is a multiple of 11. |
| 12 | No (remainder 1) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 87721 a prime number?
Yes. 87721 is divisible only by 1 and itself.
What are the factors of 87721?
1, 87721.
What is 87721 in binary?
10101011010101001 (hexadecimal 156A9, octal 253251).
What is the square root of 87721?
About 296.1773.
Is 87721 divisible by 3?
No. Its digits add up to 25, which is not a multiple of 3.
What is special about the number 87721?
87721 is a twin prime (87719 and 87721 are both prime); the 8520th prime number; a happy number: repeatedly adding the squares of its digits reaches 1.