The number 1581
1581 is a composite number with 8 divisors. Its prime factorisation is 3 × 17 × 31. Divisors (8): 1, 3, 17, 31, 51, 93, 527, 1581.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 1581: a happy number: repeatedly adding the squares of its digits reaches 1.
- 2
1581 is composite. Its prime factorisation is
- 3
The divisors add up to 2304; without 1581 itself that is 723, so 1581 is deficient (723 is less than 1581). Euler's totient φ(1581) = 960 numbers up to 1581 share no factor with it.
- 4
The digits of 1581 add up to 15, and repeating that until one digit is left gives the digital root 6. The Collatz sequence (halve if even, else 3n+1) takes 78 steps to reach 1.
LaTeX source of the formulas on this page
\[ 1581 = 3 \times 17 \times 31 \]
1581 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 8 |
| Sum of divisors | 2304 |
| Euler totient φ(n) | 960 |
| Square | 2499561 |
| Cube | 3951805941 |
| Square root | 39.761791 |
| Digit sum / digital root | 15 / 6 |
| Collatz steps to 1 | 78 |
| Scientific notation | 1.581 × |
1581 in other forms
| Form | Value |
|---|---|
| In words | one thousand five hundred and eighty-one |
| Roman numerals | MDLXXXI |
| Binary (base 2) | 11000101101 |
| Octal (base 8) | 3055 |
| Hexadecimal (base 16) | 62D |
| Base 3 | 2011120 |
| As time | 1581 seconds = 26 min 21 s |
Is 1581 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 (1581 ÷ 3 = 527) | 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 | 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 5) | A number is divisible by 8 if the last three digits make a multiple of 8. |
| 9 | No (remainder 6) | 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 8) | 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 1581 a prime number?
No. 1581 = 3 × 17 × 31, so it is divisible by 3.
What are the factors of 1581?
1, 3, 17, 31, 51, 93, 527, 1581.
What is 1581 in binary?
11000101101 (hexadecimal 62D, octal 3055).
What is the square root of 1581?
About 39.7618.
What is 1581 in Roman numerals?
MDLXXXI.
Is 1581 divisible by 3?
Yes. Its digits add up to 15, a multiple of 3.
What is special about the number 1581?
1581 is a happy number: repeatedly adding the squares of its digits reaches 1.