The number 16561
16561 is a palindromic prime: it reads the same backwards and is prime, the 1917th prime number and a palindrome: it reads 16561 backwards too. Its only divisors are 1 and 16561.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 16561: a palindromic prime: it reads the same backwards and is prime; the 1917th prime number; a palindrome: it reads 16561 backwards too.
- 2
16561 is prime, so its only factors are 1 and 16561. It is the 1917th prime; the next prime is 16567 and the one before is 16553.
- 3
The divisors add up to 16562; without 16561 itself that is 1, so 16561 is deficient (1 is less than 16561). Euler's totient φ(16561) = 16560 numbers up to 16561 share no factor with it.
- 4
The digits of 16561 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 159 steps to reach 1.
16561 at a glance
| Property | Value |
|---|---|
| Type | prime |
| Number of divisors | 2 |
| Sum of divisors | 16562 |
| Euler totient φ(n) | 16560 |
| Square | 274266721 |
| Cube | 4542131166481 |
| Square root | 128.689549 |
| Digit sum / digital root | 19 / 1 |
| Collatz steps to 1 | 159 |
| Scientific notation | 1.6561 × |
16561 in other forms
| Form | Value |
|---|---|
| In words | sixteen thousand five hundred and sixty-one |
| Binary (base 2) | 100000010110001 |
| Octal (base 8) | 40261 |
| Hexadecimal (base 16) | 40B1 |
| Base 3 | 211201101 |
| As time | 16561 seconds = 4 h 36 min 1 s |
Is 16561 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 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 | 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 6) | 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 16561 a prime number?
Yes. 16561 is divisible only by 1 and itself.
What are the factors of 16561?
1, 16561.
What is 16561 in binary?
100000010110001 (hexadecimal 40B1, octal 40261).
What is the square root of 16561?
About 128.6895.
Is 16561 divisible by 3?
No. Its digits add up to 19, which is not a multiple of 3.
What is special about the number 16561?
16561 is a palindromic prime: it reads the same backwards and is prime; the 1917th prime number; a palindrome: it reads 16561 backwards too.