The number 2181
2181 is a composite number with 4 divisors. Its prime factorisation is 3 × 727. Divisors (4): 1, 3, 727, 2181.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 2181: a happy number: repeatedly adding the squares of its digits reaches 1; a semiprime: 3 × 727, the product of two primes.
- 2
2181 is composite. Its prime factorisation is
- 3
The divisors add up to 2912; without 2181 itself that is 731, so 2181 is deficient (731 is less than 2181). Euler's totient φ(2181) = 1452 numbers up to 2181 share no factor with it.
- 4
The digits of 2181 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 45 steps to reach 1.
LaTeX source of the formulas on this page
\[ 2181 = 3 \times 727 \]
2181 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 4 |
| Sum of divisors | 2912 |
| Euler totient φ(n) | 1452 |
| Square | 4756761 |
| Cube | 10374495741 |
| Square root | 46.701178 |
| Digit sum / digital root | 12 / 3 |
| Collatz steps to 1 | 45 |
| Scientific notation | 2.181 × |
2181 in other forms
| Form | Value |
|---|---|
| In words | two thousand one hundred and eighty-one |
| Roman numerals | MMCLXXXI |
| Binary (base 2) | 100010000101 |
| Octal (base 8) | 4205 |
| Hexadecimal (base 16) | 885 |
| Base 3 | 2222210 |
| As time | 2181 seconds = 36 min 21 s |
Is 2181 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 (2181 ÷ 3 = 727) | 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 4) | 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 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 3) | 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 2181 a prime number?
No. 2181 = 3 × 727, so it is divisible by 3.
What are the factors of 2181?
1, 3, 727, 2181.
What is 2181 in binary?
100010000101 (hexadecimal 885, octal 4205).
What is the square root of 2181?
About 46.7012.
What is 2181 in Roman numerals?
MMCLXXXI.
Is 2181 divisible by 3?
Yes. Its digits add up to 12, a multiple of 3.
What is special about the number 2181?
2181 is a happy number: repeatedly adding the squares of its digits reaches 1; a semiprime: 3 × 727, the product of two primes.