The number 1661
1661 is a palindrome: it reads 1661 backwards too. Its prime factorisation is 11 × 151. Divisors (4): 1, 11, 151, 1661.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 1661: a palindrome: it reads 1661 backwards too; a semiprime: 11 × 151, the product of two primes.
- 2
1661 is composite. Its prime factorisation is
- 3
The divisors add up to 1824; without 1661 itself that is 163, so 1661 is deficient (163 is less than 1661). Euler's totient φ(1661) = 1500 numbers up to 1661 share no factor with it.
- 4
The digits of 1661 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 135 steps to reach 1.
LaTeX source of the formulas on this page
\[ 1661 = 11 \times 151 \]
1661 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 4 |
| Sum of divisors | 1824 |
| Euler totient φ(n) | 1500 |
| Square | 2758921 |
| Cube | 4582567781 |
| Square root | 40.755368 |
| Digit sum / digital root | 14 / 5 |
| Collatz steps to 1 | 135 |
| Scientific notation | 1.661 × |
1661 in other forms
| Form | Value |
|---|---|
| In words | one thousand six hundred and sixty-one |
| Roman numerals | MDCLXI |
| Binary (base 2) | 11001111101 |
| Octal (base 8) | 3175 |
| Hexadecimal (base 16) | 67D |
| Base 3 | 2021112 |
| As time | 1661 seconds = 27 min 41 s |
Is 1661 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 | No (remainder 2) | 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 | Yes (1661 ÷ 11 = 151) | 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 1661 a prime number?
No. 1661 = 11 × 151, so it is divisible by 11.
What are the factors of 1661?
1, 11, 151, 1661.
What is 1661 in binary?
11001111101 (hexadecimal 67D, octal 3175).
What is the square root of 1661?
About 40.7554.
What is 1661 in Roman numerals?
MDCLXI.
Is 1661 divisible by 3?
No. Its digits add up to 14, which is not a multiple of 3.
What is special about the number 1661?
1661 is a palindrome: it reads 1661 backwards too; a semiprime: 11 × 151, the product of two primes.