The number 15561
15561 is a composite number with 24 divisors. Its prime factorisation is × 7 × 13 × 19. Divisors (24): 1, 3, 7, 9, 13, 19, 21, 39, 57, 63, 91, 117, 133, 171, 247, 273 … 15561.
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How to work it out
- 1
15561 has no famous special property in the usual lists (prime, square, cube, triangular, Fibonacci, palindrome, perfect), but it is still a composite number.
- 2
15561 is composite. Its prime factorisation is
- 3
The divisors add up to 29120; without 15561 itself that is 13559, so 15561 is deficient (13559 is less than 15561). Euler's totient φ(15561) = 7776 numbers up to 15561 share no factor with it.
- 4
The digits of 15561 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 84 steps to reach 1.
LaTeX source of the formulas on this page
\[ 15561 = 3^{2} \times 7 \times 13 \times 19 \]15561 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 24 |
| Sum of divisors | 29120 |
| Euler totient φ(n) | 7776 |
| Square | 242144721 |
| Cube | 3768014003481 |
| Square root | 124.743737 (= 3√1729) |
| Digit sum / digital root | 18 / 9 |
| Collatz steps to 1 | 84 |
| Scientific notation | 1.5561 × |
15561 in other forms
| Form | Value |
|---|---|
| In words | fifteen thousand five hundred and sixty-one |
| Binary (base 2) | 11110011001001 |
| Octal (base 8) | 36311 |
| Hexadecimal (base 16) | 3CC9 |
| Base 3 | 210100100 |
| As time | 15561 seconds = 4 h 19 min 21 s |
Is 15561 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 (15561 ÷ 3 = 5187) | 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 | Yes (15561 ÷ 7 = 2223) | 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 (15561 ÷ 9 = 1729) | 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 9) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 15561 a prime number?
No. 15561 = × 7 × 13 × 19, so it is divisible by 3.
What are the factors of 15561?
1, 3, 7, 9, 13, 19, 21, 39, 57, 63, 91, 117, 133, 171, 247, 273, 399, 741, 819, 1197, 1729, 2223, 5187, 15561.
What is 15561 in binary?
11110011001001 (hexadecimal 3CC9, octal 36311).
What is the square root of 15561?
About 124.7437, exactly 3√1729.
Is 15561 divisible by 3?
Yes. Its digits add up to 18, a multiple of 3.
What is special about the number 15561?
It is a composite number with 24 divisors.