The number 81221
81221 is a composite number with 8 divisors. Its prime factorisation is 7 × 41 × 283. Divisors (8): 1, 7, 41, 283, 287, 1981, 11603, 81221.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
81221 has no famous special property in the usual lists (prime, square, cube, triangular, Fibonacci, palindrome, perfect), but it is still a composite number.
- 2
81221 is composite. Its prime factorisation is
- 3
The divisors add up to 95424; without 81221 itself that is 14203, so 81221 is deficient (14203 is less than 81221). Euler's totient φ(81221) = 67680 numbers up to 81221 share no factor with it.
- 4
The digits of 81221 add up to 14, and repeating that until one digit is left gives the digital root 5. The Collatz sequence (halve if even, else 3n+1) takes 138 steps to reach 1.
LaTeX source of the formulas on this page
\[ 81221 = 7 \times 41 \times 283 \]
81221 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 8 |
| Sum of divisors | 95424 |
| Euler totient φ(n) | 67680 |
| Square | 6596850841 |
| Cube | 535802822156861 |
| Square root | 284.992982 |
| Digit sum / digital root | 14 / 5 |
| Collatz steps to 1 | 138 |
| Scientific notation | 8.1221 × |
81221 in other forms
| Form | Value |
|---|---|
| In words | eighty-one thousand two hundred and twenty-one |
| Binary (base 2) | 10011110101000101 |
| Octal (base 8) | 236505 |
| Hexadecimal (base 16) | 13D45 |
| Base 3 | 11010102012 |
| As time | 81221 seconds = 22 h 33 min 41 s |
Is 81221 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 | Yes (81221 ÷ 7 = 11603) | 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 5) | 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 8) | 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 81221 a prime number?
No. 81221 = 7 × 41 × 283, so it is divisible by 7.
What are the factors of 81221?
1, 7, 41, 283, 287, 1981, 11603, 81221.
What is 81221 in binary?
10011110101000101 (hexadecimal 13D45, octal 236505).
What is the square root of 81221?
About 284.9930.
Is 81221 divisible by 3?
No. Its digits add up to 14, which is not a multiple of 3.
What is special about the number 81221?
It is a composite number with 8 divisors.