The number 161
161 is a palindrome: it reads 161 backwards too. Its prime factorisation is 7 × 23. Divisors (4): 1, 7, 23, 161.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 161: a palindrome: it reads 161 backwards too; a semiprime: 7 × 23, the product of two primes.
- 2
161 is composite. Its prime factorisation is
- 3
The divisors add up to 192; without 161 itself that is 31, so 161 is deficient (31 is less than 161). Euler's totient φ(161) = 132 numbers up to 161 share no factor with it.
- 4
The digits of 161 add up to 8, and repeating that until one digit is left gives the digital root 8. The Collatz sequence (halve if even, else 3n+1) takes 98 steps to reach 1.
LaTeX source of the formulas on this page
\[ 161 = 7 \times 23 \]
161 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 4 |
| Sum of divisors | 192 |
| Euler totient φ(n) | 132 |
| Square | 25921 |
| Cube | 4173281 |
| Square root | 12.688578 |
| Digit sum / digital root | 8 / 8 |
| Collatz steps to 1 | 98 |
| Scientific notation | 1.61 × |
161 in other forms
| Form | Value |
|---|---|
| In words | one hundred and sixty-one |
| Roman numerals | CLXI |
| Binary (base 2) | 10100001 |
| Octal (base 8) | 241 |
| Hexadecimal (base 16) | A1 |
| Base 3 | 12222 |
| As time | 161 seconds = 2 min 41 s |
Is 161 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 (161 ÷ 7 = 23) | 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 1) | A number is divisible by 8 if the last three digits make a multiple of 8. |
| 9 | No (remainder 8) | 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 5) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 161 a prime number?
No. 161 = 7 × 23, so it is divisible by 7.
What are the factors of 161?
1, 7, 23, 161.
What is 161 in binary?
10100001 (hexadecimal A1, octal 241).
What is the square root of 161?
About 12.6886.
What is 161 in Roman numerals?
CLXI.
Is 161 divisible by 3?
No. Its digits add up to 8, which is not a multiple of 3.
What is special about the number 161?
161 is a palindrome: it reads 161 backwards too; a semiprime: 7 × 23, the product of two primes.