The number 65521
65521 is a twin prime (65519 and 65521 are both prime) and the 6542nd prime number. Its only divisors are 1 and 65521.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 65521: a twin prime (65519 and 65521 are both prime); the 6542nd prime number; a happy number: repeatedly adding the squares of its digits reaches 1.
- 2
65521 is prime, so its only factors are 1 and 65521. It is the 6542nd prime; the next prime is 65537 and the one before is 65519.
- 3
The divisors add up to 65522; without 65521 itself that is 1, so 65521 is deficient (1 is less than 65521). Euler's totient φ(65521) = 65520 numbers up to 65521 share no factor with it.
- 4
The digits of 65521 add up to 19, and repeating that until one digit is left gives the digital root 1. The Collatz sequence (halve if even, else 3n+1) takes 161 steps to reach 1.
65521 at a glance
| Property | Value |
|---|---|
| Type | prime |
| Number of divisors | 2 |
| Sum of divisors | 65522 |
| Euler totient φ(n) | 65520 |
| Square | 4293001441 |
| Cube | 281281747415761 |
| Square root | 255.970701 |
| Digit sum / digital root | 19 / 1 |
| Collatz steps to 1 | 161 |
| Scientific notation | 6.5521 × |
65521 in other forms
| Form | Value |
|---|---|
| In words | sixty-five thousand five hundred and twenty-one |
| Binary (base 2) | 1111111111110001 |
| Octal (base 8) | 177761 |
| Hexadecimal (base 16) | FFF1 |
| Base 3 | 10022212201 |
| As time | 65521 seconds = 18 h 12 min 1 s |
Is 65521 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 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 1) | A number is divisible by 8 if the last three digits make a multiple of 8. |
| 9 | No (remainder 1) | 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 1) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 65521 a prime number?
Yes. 65521 is divisible only by 1 and itself.
What are the factors of 65521?
1, 65521.
What is 65521 in binary?
1111111111110001 (hexadecimal FFF1, octal 177761).
What is the square root of 65521?
About 255.9707.
Is 65521 divisible by 3?
No. Its digits add up to 19, which is not a multiple of 3.
What is special about the number 65521?
65521 is a twin prime (65519 and 65521 are both prime); the 6542nd prime number; a happy number: repeatedly adding the squares of its digits reaches 1.