The number 61981
61981 is a twin prime (61979 and 61981 are both prime) and the 6230th prime number. Its only divisors are 1 and 61981.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 61981: a twin prime (61979 and 61981 are both prime); the 6230th prime number.
- 2
61981 is prime, so its only factors are 1 and 61981. It is the 6230th prime; the next prime is 61987 and the one before is 61979.
- 3
The divisors add up to 61982; without 61981 itself that is 1, so 61981 is deficient (1 is less than 61981). Euler's totient φ(61981) = 61980 numbers up to 61981 share no factor with it.
- 4
The digits of 61981 add up to 25, and repeating that until one digit is left gives the digital root 7. The Collatz sequence (halve if even, else 3n+1) takes 117 steps to reach 1.
61981 at a glance
| Property | Value |
|---|---|
| Type | prime |
| Number of divisors | 2 |
| Sum of divisors | 61982 |
| Euler totient φ(n) | 61980 |
| Square | 3841644361 |
| Cube | 238108959139141 |
| Square root | 248.959836 |
| Digit sum / digital root | 25 / 7 |
| Collatz steps to 1 | 117 |
| Scientific notation | 6.1981 × |
61981 in other forms
| Form | Value |
|---|---|
| In words | sixty-one thousand nine hundred and eighty-one |
| Binary (base 2) | 1111001000011101 |
| Octal (base 8) | 171035 |
| Hexadecimal (base 16) | F21D |
| Base 3 | 10011000121 |
| As time | 61981 seconds = 17 h 13 min 1 s |
Is 61981 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 1) | 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 1) | A number is divisible by 6 if it is divisible by both 2 and 3. |
| 7 | No (remainder 3) | 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 7) | 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 1) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 61981 a prime number?
Yes. 61981 is divisible only by 1 and itself.
What are the factors of 61981?
1, 61981.
What is 61981 in binary?
1111001000011101 (hexadecimal F21D, octal 171035).
What is the square root of 61981?
About 248.9598.
Is 61981 divisible by 3?
No. Its digits add up to 25, which is not a multiple of 3.
What is special about the number 61981?
61981 is a twin prime (61979 and 61981 are both prime); the 6230th prime number.