The number 8721
8721 is a binary palindrome (10001000010001). Its prime factorisation is × 17 × 19. Divisors (16): 1, 3, 9, 17, 19, 27, 51, 57, 153, 171, 323, 459, 513, 969, 2907, 8721.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 8721: a binary palindrome (10001000010001).
- 2
8721 is composite. Its prime factorisation is
- 3
The divisors add up to 14400; without 8721 itself that is 5679, so 8721 is deficient (5679 is less than 8721). Euler's totient φ(8721) = 5184 numbers up to 8721 share no factor with it.
- 4
The digits of 8721 add up to 18, and repeating that until one digit is left gives the digital root 9. The Collatz sequence (halve if even, else 3n+1) takes 47 steps to reach 1.
LaTeX source of the formulas on this page
\[ 8721 = 3^{3} \times 17 \times 19 \]8721 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 16 |
| Sum of divisors | 14400 |
| Euler totient φ(n) | 5184 |
| Square | 76055841 |
| Cube | 663282989361 |
| Square root | 93.386294 (= 3√969) |
| Digit sum / digital root | 18 / 9 |
| Collatz steps to 1 | 47 |
| Scientific notation | 8.721 × |
8721 in other forms
| Form | Value |
|---|---|
| In words | eight thousand seven hundred and twenty-one |
| Binary (base 2) | 10001000010001 |
| Octal (base 8) | 21021 |
| Hexadecimal (base 16) | 2211 |
| Base 3 | 102222000 |
| As time | 8721 seconds = 2 h 25 min 21 s |
Is 8721 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 | Yes (8721 ÷ 3 = 2907) | 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 3) | A number is divisible by 6 if it is divisible by both 2 and 3. |
| 7 | No (remainder 6) | 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 | Yes (8721 ÷ 9 = 969) | 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 9) | A number is divisible by 11 if the alternating sum of the digits is a multiple of 11. |
| 12 | No (remainder 9) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 8721 a prime number?
No. 8721 = × 17 × 19, so it is divisible by 3.
What are the factors of 8721?
1, 3, 9, 17, 19, 27, 51, 57, 153, 171, 323, 459, 513, 969, 2907, 8721.
What is 8721 in binary?
10001000010001 (hexadecimal 2211, octal 21021).
What is the square root of 8721?
About 93.3863, exactly 3√969.
Is 8721 divisible by 3?
Yes. Its digits add up to 18, a multiple of 3.
What is special about the number 8721?
8721 is a binary palindrome (10001000010001).