The number 81990
81990 is a composite number with 24 divisors. Its prime factorisation is 2 × × 5 × 911. Divisors (24): 1, 2, 3, 5, 6, 9, 10, 15, 18, 30, 45, 90, 911, 1822, 2733, 4555 … 81990.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
81990 has no famous special property in the usual lists (prime, square, cube, triangular, Fibonacci, palindrome, perfect), but it is still a composite number.
- 2
81990 is composite. Its prime factorisation is
- 3
The divisors add up to 213408; without 81990 itself that is 131418, so 81990 is abundant (131418 is more than 81990). Euler's totient φ(81990) = 21840 numbers up to 81990 share no factor with it.
- 4
The digits of 81990 add up to 27, and repeating that until one digit is left gives the digital root 9. The Collatz sequence (halve if even, else 3n+1) takes 151 steps to reach 1.
LaTeX source of the formulas on this page
\[ 81990 = 2 \times 3^{2} \times 5 \times 911 \]81990 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 24 |
| Sum of divisors | 213408 |
| Euler totient φ(n) | 21840 |
| Square | 6722360100 |
| Cube | 551166304599000 |
| Square root | 286.338960 (= 3√9110) |
| Digit sum / digital root | 27 / 9 |
| Collatz steps to 1 | 151 |
| Scientific notation | 8.199 × |
81990 in other forms
| Form | Value |
|---|---|
| In words | eighty-one thousand nine hundred and ninety |
| Binary (base 2) | 10100000001000110 |
| Octal (base 8) | 240106 |
| Hexadecimal (base 16) | 14046 |
| Base 3 | 11011110200 |
| As time | 81990 seconds = 22 h 46 min 30 s |
Is 81990 divisible by 2 to 12?
| Divisor | Answer | Rule |
|---|---|---|
| 2 | Yes (81990 ÷ 2 = 40995) | A number is divisible by 2 if the last digit is even (0, 2, 4, 6, 8). |
| 3 | Yes (81990 ÷ 3 = 27330) | A number is divisible by 3 if the digits add up to a multiple of 3. |
| 4 | No (remainder 2) | A number is divisible by 4 if the last two digits make a multiple of 4. |
| 5 | Yes (81990 ÷ 5 = 16398) | A number is divisible by 5 if the last digit is 0 or 5. |
| 6 | Yes (81990 ÷ 6 = 13665) | 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 6) | A number is divisible by 8 if the last three digits make a multiple of 8. |
| 9 | Yes (81990 ÷ 9 = 9110) | A number is divisible by 9 if the digits add up to a multiple of 9. |
| 10 | Yes (81990 ÷ 10 = 8199) | 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 6) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 81990 a prime number?
No. 81990 = 2 × × 5 × 911, so it is divisible by 2.
What are the factors of 81990?
1, 2, 3, 5, 6, 9, 10, 15, 18, 30, 45, 90, 911, 1822, 2733, 4555, 5466, 8199, 9110, 13665, 16398, 27330, 40995, 81990.
What is 81990 in binary?
10100000001000110 (hexadecimal 14046, octal 240106).
What is the square root of 81990?
About 286.3390, exactly 3√9110.
Is 81990 divisible by 3?
Yes. Its digits add up to 27, a multiple of 3.
What is special about the number 81990?
It is a composite number with 24 divisors.