The number 1281
1281 is a composite number with 8 divisors. Its prime factorisation is 3 × 7 × 61. Divisors (8): 1, 3, 7, 21, 61, 183, 427, 1281.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 1281: a happy number: repeatedly adding the squares of its digits reaches 1.
- 2
1281 is composite. Its prime factorisation is
- 3
The divisors add up to 1984; without 1281 itself that is 703, so 1281 is deficient (703 is less than 1281). Euler's totient φ(1281) = 720 numbers up to 1281 share no factor with it.
- 4
The digits of 1281 add up to 12, and repeating that until one digit is left gives the digital root 3. The Collatz sequence (halve if even, else 3n+1) takes 52 steps to reach 1.
LaTeX source of the formulas on this page
\[ 1281 = 3 \times 7 \times 61 \]
1281 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 8 |
| Sum of divisors | 1984 |
| Euler totient φ(n) | 720 |
| Square | 1640961 |
| Cube | 2102071041 |
| Square root | 35.791060 |
| Digit sum / digital root | 12 / 3 |
| Collatz steps to 1 | 52 |
| Scientific notation | 1.281 × |
1281 in other forms
| Form | Value |
|---|---|
| In words | one thousand two hundred and eighty-one |
| Roman numerals | MCCLXXXI |
| Binary (base 2) | 10100000001 |
| Octal (base 8) | 2401 |
| Hexadecimal (base 16) | 501 |
| Base 3 | 1202110 |
| As time | 1281 seconds = 21 min 21 s |
Is 1281 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 (1281 ÷ 3 = 427) | 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 (1281 ÷ 7 = 183) | 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 3) | 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 9) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 1281 a prime number?
No. 1281 = 3 × 7 × 61, so it is divisible by 3.
What are the factors of 1281?
1, 3, 7, 21, 61, 183, 427, 1281.
What is 1281 in binary?
10100000001 (hexadecimal 501, octal 2401).
What is the square root of 1281?
About 35.7911.
What is 1281 in Roman numerals?
MCCLXXXI.
Is 1281 divisible by 3?
Yes. Its digits add up to 12, a multiple of 3.
What is special about the number 1281?
1281 is a happy number: repeatedly adding the squares of its digits reaches 1.