The number 81220
81220 is a composite number with 24 divisors. Its prime factorisation is × 5 × 31 × 131. Divisors (24): 1, 2, 4, 5, 10, 20, 31, 62, 124, 131, 155, 262, 310, 524, 620, 655 … 81220.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
81220 has no famous special property in the usual lists (prime, square, cube, triangular, Fibonacci, palindrome, perfect), but it is still a composite number.
- 2
81220 is composite. Its prime factorisation is
- 3
The divisors add up to 177408; without 81220 itself that is 96188, so 81220 is abundant (96188 is more than 81220). Euler's totient φ(81220) = 31200 numbers up to 81220 share no factor with it.
- 4
The digits of 81220 add up to 13, and repeating that until one digit is left gives the digital root 4. The Collatz sequence (halve if even, else 3n+1) takes 138 steps to reach 1.
LaTeX source of the formulas on this page
\[ 81220 = 2^{2} \times 5 \times 31 \times 131 \]81220 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 24 |
| Sum of divisors | 177408 |
| Euler totient φ(n) | 31200 |
| Square | 6596688400 |
| Cube | 535783031848000 |
| Square root | 284.991228 (= 2√20305) |
| Digit sum / digital root | 13 / 4 |
| Collatz steps to 1 | 138 |
| Scientific notation | 8.122 × |
81220 in other forms
| Form | Value |
|---|---|
| In words | eighty-one thousand two hundred and twenty |
| Binary (base 2) | 10011110101000100 |
| Octal (base 8) | 236504 |
| Hexadecimal (base 16) | 13D44 |
| Base 3 | 11010102011 |
| As time | 81220 seconds = 22 h 33 min 40 s |
Is 81220 divisible by 2 to 12?
| Divisor | Answer | Rule |
|---|---|---|
| 2 | Yes (81220 ÷ 2 = 40610) | A number is divisible by 2 if the last digit is even (0, 2, 4, 6, 8). |
| 3 | No (remainder 1) | A number is divisible by 3 if the digits add up to a multiple of 3. |
| 4 | Yes (81220 ÷ 4 = 20305) | A number is divisible by 4 if the last two digits make a multiple of 4. |
| 5 | Yes (81220 ÷ 5 = 16244) | A number is divisible by 5 if the last digit is 0 or 5. |
| 6 | No (remainder 4) | 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 4) | A number is divisible by 8 if the last three digits make a multiple of 8. |
| 9 | No (remainder 4) | A number is divisible by 9 if the digits add up to a multiple of 9. |
| 10 | Yes (81220 ÷ 10 = 8122) | 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 4) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 81220 a prime number?
No. 81220 = × 5 × 31 × 131, so it is divisible by 2.
What are the factors of 81220?
1, 2, 4, 5, 10, 20, 31, 62, 124, 131, 155, 262, 310, 524, 620, 655, 1310, 2620, 4061, 8122, 16244, 20305, 40610, 81220.
What is 81220 in binary?
10011110101000100 (hexadecimal 13D44, octal 236504).
What is the square root of 81220?
About 284.9912, exactly 2√20305.
Is 81220 divisible by 3?
No. Its digits add up to 13, which is not a multiple of 3.
What is special about the number 81220?
It is a composite number with 24 divisors.