The number 217
217 is a composite number with 4 divisors. Its prime factorisation is 7 × 31. Divisors (4): 1, 7, 31, 217.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 217: a semiprime: 7 × 31, the product of two primes.
- 2
217 is composite. Its prime factorisation is
- 3
The divisors add up to 256; without 217 itself that is 39, so 217 is deficient (39 is less than 217). Euler's totient φ(217) = 180 numbers up to 217 share no factor with it.
- 4
The digits of 217 add up to 10, and repeating that until one digit is left gives the digital root 1. The Collatz sequence (halve if even, else 3n+1) takes 26 steps to reach 1.
LaTeX source of the formulas on this page
\[ 217 = 7 \times 31 \]
217 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 4 |
| Sum of divisors | 256 |
| Euler totient φ(n) | 180 |
| Square | 47089 |
| Cube | 10218313 |
| Square root | 14.730920 |
| Digit sum / digital root | 10 / 1 |
| Collatz steps to 1 | 26 |
| Scientific notation | 2.17 × |
217 in other forms
| Form | Value |
|---|---|
| In words | two hundred and seventeen |
| Roman numerals | CCXVII |
| Binary (base 2) | 11011001 |
| Octal (base 8) | 331 |
| Hexadecimal (base 16) | D9 |
| Base 3 | 22001 |
| As time | 217 seconds = 3 min 37 s |
Is 217 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 2) | 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 | Yes (217 ÷ 7 = 31) | 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 1) | A number is divisible by 9 if the digits add up to a multiple of 9. |
| 10 | No (remainder 7) | 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 1) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 217 a prime number?
No. 217 = 7 × 31, so it is divisible by 7.
What are the factors of 217?
1, 7, 31, 217.
What is 217 in binary?
11011001 (hexadecimal D9, octal 331).
What is the square root of 217?
About 14.7309.
What is 217 in Roman numerals?
CCXVII.
Is 217 divisible by 3?
No. Its digits add up to 10, which is not a multiple of 3.
What is special about the number 217?
217 is a semiprime: 7 × 31, the product of two primes.