The number 1781
1781 is a composite number with 4 divisors. Its prime factorisation is 13 × 137. Divisors (4): 1, 13, 137, 1781.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 1781: a semiprime: 13 × 137, the product of two primes.
- 2
1781 is composite. Its prime factorisation is
- 3
The divisors add up to 1932; without 1781 itself that is 151, so 1781 is deficient (151 is less than 1781). Euler's totient φ(1781) = 1632 numbers up to 1781 share no factor with it.
- 4
The digits of 1781 add up to 17, and repeating that until one digit is left gives the digital root 8. The Collatz sequence (halve if even, else 3n+1) takes 73 steps to reach 1.
LaTeX source of the formulas on this page
\[ 1781 = 13 \times 137 \]
1781 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 4 |
| Sum of divisors | 1932 |
| Euler totient φ(n) | 1632 |
| Square | 3171961 |
| Cube | 5649262541 |
| Square root | 42.201896 |
| Digit sum / digital root | 17 / 8 |
| Collatz steps to 1 | 73 |
| Scientific notation | 1.781 × |
1781 in other forms
| Form | Value |
|---|---|
| In words | one thousand seven hundred and eighty-one |
| Roman numerals | MDCCLXXXI |
| Binary (base 2) | 11011110101 |
| Octal (base 8) | 3365 |
| Hexadecimal (base 16) | 6F5 |
| Base 3 | 2102222 |
| As time | 1781 seconds = 29 min 41 s |
Is 1781 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 3) | 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 8) | 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 5) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 1781 a prime number?
No. 1781 = 13 × 137, so it is divisible by 13.
What are the factors of 1781?
1, 13, 137, 1781.
What is 1781 in binary?
11011110101 (hexadecimal 6F5, octal 3365).
What is the square root of 1781?
About 42.2019.
What is 1781 in Roman numerals?
MDCCLXXXI.
Is 1781 divisible by 3?
No. Its digits add up to 17, which is not a multiple of 3.
What is special about the number 1781?
1781 is a semiprime: 13 × 137, the product of two primes.