The number 2561
2561 is a composite number with 4 divisors. Its prime factorisation is 13 × 197. Divisors (4): 1, 13, 197, 2561.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 2561: a semiprime: 13 × 197, the product of two primes.
- 2
2561 is composite. Its prime factorisation is
- 3
The divisors add up to 2772; without 2561 itself that is 211, so 2561 is deficient (211 is less than 2561). Euler's totient φ(2561) = 2352 numbers up to 2561 share no factor with it.
- 4
The digits of 2561 add up to 14, and repeating that until one digit is left gives the digital root 5. The Collatz sequence (halve if even, else 3n+1) takes 146 steps to reach 1.
LaTeX source of the formulas on this page
\[ 2561 = 13 \times 197 \]
2561 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 4 |
| Sum of divisors | 2772 |
| Euler totient φ(n) | 2352 |
| Square | 6558721 |
| Cube | 16796884481 |
| Square root | 50.606324 |
| Digit sum / digital root | 14 / 5 |
| Collatz steps to 1 | 146 |
| Scientific notation | 2.561 × |
2561 in other forms
| Form | Value |
|---|---|
| In words | two thousand five hundred and sixty-one |
| Roman numerals | MMDLXI |
| Binary (base 2) | 101000000001 |
| Octal (base 8) | 5001 |
| Hexadecimal (base 16) | A01 |
| Base 3 | 10111212 |
| As time | 2561 seconds = 42 min 41 s |
Is 2561 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 2) | 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 5) | 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 5) | 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 5) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 2561 a prime number?
No. 2561 = 13 × 197, so it is divisible by 13.
What are the factors of 2561?
1, 13, 197, 2561.
What is 2561 in binary?
101000000001 (hexadecimal A01, octal 5001).
What is the square root of 2561?
About 50.6063.
What is 2561 in Roman numerals?
MMDLXI.
Is 2561 divisible by 3?
No. Its digits add up to 14, which is not a multiple of 3.
What is special about the number 2561?
2561 is a semiprime: 13 × 197, the product of two primes.