The number 209
209 is a composite number with 4 divisors. Its prime factorisation is 11 × 19. Divisors (4): 1, 11, 19, 209.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 209: a Harshad number: divisible by its digit sum 11; a semiprime: 11 × 19, the product of two primes.
- 2
209 is composite. Its prime factorisation is
- 3
The divisors add up to 240; without 209 itself that is 31, so 209 is deficient (31 is less than 209). Euler's totient φ(209) = 180 numbers up to 209 share no factor with it.
- 4
The digits of 209 add up to 11, and repeating that until one digit is left gives the digital root 2. The Collatz sequence (halve if even, else 3n+1) takes 39 steps to reach 1.
LaTeX source of the formulas on this page
\[ 209 = 11 \times 19 \]
209 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 4 |
| Sum of divisors | 240 |
| Euler totient φ(n) | 180 |
| Square | 43681 |
| Cube | 9129329 |
| Square root | 14.456832 |
| Digit sum / digital root | 11 / 2 |
| Collatz steps to 1 | 39 |
| Scientific notation | 2.09 × |
209 in other forms
| Form | Value |
|---|---|
| In words | two hundred and nine |
| Roman numerals | CCIX |
| Binary (base 2) | 11010001 |
| Octal (base 8) | 321 |
| Hexadecimal (base 16) | D1 |
| Base 3 | 21202 |
| As time | 209 seconds = 3 min 29 s |
Is 209 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 4) | 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 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 1) | A number is divisible by 8 if the last three digits make a multiple of 8. |
| 9 | No (remainder 2) | A number is divisible by 9 if the digits add up to a multiple of 9. |
| 10 | No (remainder 9) | A number is divisible by 10 if the last digit is 0. |
| 11 | Yes (209 ÷ 11 = 19) | 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 209 a prime number?
No. 209 = 11 × 19, so it is divisible by 11.
What are the factors of 209?
1, 11, 19, 209.
What is 209 in binary?
11010001 (hexadecimal D1, octal 321).
What is the square root of 209?
About 14.4568.
What is 209 in Roman numerals?
CCIX.
Is 209 divisible by 3?
No. Its digits add up to 11, which is not a multiple of 3.
What is special about the number 209?
209 is a Harshad number: divisible by its digit sum 11; a semiprime: 11 × 19, the product of two primes.