The number 20181
20181 is a composite number with 12 divisors. Its prime factorisation is 3 × 7 × . Divisors (12): 1, 3, 7, 21, 31, 93, 217, 651, 961, 2883, 6727, 20181.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 20181: a happy number: repeatedly adding the squares of its digits reaches 1.
- 2
20181 is composite. Its prime factorisation is
- 3
The divisors add up to 31776; without 20181 itself that is 11595, so 20181 is deficient (11595 is less than 20181). Euler's totient φ(20181) = 11160 numbers up to 20181 share no factor with it.
- 4
The digits of 20181 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 43 steps to reach 1.
LaTeX source of the formulas on this page
\[ 20181 = 3 \times 7 \times 31^{2} \]20181 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 12 |
| Sum of divisors | 31776 |
| Euler totient φ(n) | 11160 |
| Square | 407272761 |
| Cube | 8219171589741 |
| Square root | 142.059847 (= 31√21) |
| Digit sum / digital root | 12 / 3 |
| Collatz steps to 1 | 43 |
| Scientific notation | 2.0181 × |
20181 in other forms
| Form | Value |
|---|---|
| In words | twenty thousand one hundred and eighty-one |
| Binary (base 2) | 100111011010101 |
| Octal (base 8) | 47325 |
| Hexadecimal (base 16) | 4ED5 |
| Base 3 | 1000200110 |
| As time | 20181 seconds = 5 h 36 min 21 s |
Is 20181 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 (20181 ÷ 3 = 6727) | 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 (20181 ÷ 7 = 2883) | 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 7) | 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 20181 a prime number?
No. 20181 = 3 × 7 × , so it is divisible by 3.
What are the factors of 20181?
1, 3, 7, 21, 31, 93, 217, 651, 961, 2883, 6727, 20181.
What is 20181 in binary?
100111011010101 (hexadecimal 4ED5, octal 47325).
What is the square root of 20181?
About 142.0598, exactly 31√21.
Is 20181 divisible by 3?
Yes. Its digits add up to 12, a multiple of 3.
What is special about the number 20181?
20181 is a happy number: repeatedly adding the squares of its digits reaches 1.