The number 1561
1561 is a composite number with 4 divisors. Its prime factorisation is 7 × 223. Divisors (4): 1, 7, 223, 1561.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 1561: a semiprime: 7 × 223, the product of two primes.
- 2
1561 is composite. Its prime factorisation is
- 3
The divisors add up to 1792; without 1561 itself that is 231, so 1561 is deficient (231 is less than 1561). Euler's totient φ(1561) = 1332 numbers up to 1561 share no factor with it.
- 4
The digits of 1561 add up to 13, and repeating that until one digit is left gives the digital root 4. The Collatz sequence (halve if even, else 3n+1) takes 60 steps to reach 1.
LaTeX source of the formulas on this page
\[ 1561 = 7 \times 223 \]
1561 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 4 |
| Sum of divisors | 1792 |
| Euler totient φ(n) | 1332 |
| Square | 2436721 |
| Cube | 3803721481 |
| Square root | 39.509493 |
| Digit sum / digital root | 13 / 4 |
| Collatz steps to 1 | 60 |
| Scientific notation | 1.561 × |
1561 in other forms
| Form | Value |
|---|---|
| In words | one thousand five hundred and sixty-one |
| Roman numerals | MDLXI |
| Binary (base 2) | 11000011001 |
| Octal (base 8) | 3031 |
| Hexadecimal (base 16) | 619 |
| Base 3 | 2010211 |
| As time | 1561 seconds = 26 min 1 s |
Is 1561 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 | Yes (1561 ÷ 7 = 223) | 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 4) | 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 10) | 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 1561 a prime number?
No. 1561 = 7 × 223, so it is divisible by 7.
What are the factors of 1561?
1, 7, 223, 1561.
What is 1561 in binary?
11000011001 (hexadecimal 619, octal 3031).
What is the square root of 1561?
About 39.5095.
What is 1561 in Roman numerals?
MDLXI.
Is 1561 divisible by 3?
No. Its digits add up to 13, which is not a multiple of 3.
What is special about the number 1561?
1561 is a semiprime: 7 × 223, the product of two primes.