Is 170 a prime number?
170 is not a prime number, because it is divisible by 2: 170 = 2 × 5 × 17, and it has 8 factors.
Checking 170 for primality, divisor by divisor
| Try | Into | Gives | Verdict |
|---|---|---|---|
| 2 | 170 | 85 remainder 0 | divides exactly |
You only need to test primes up to the square root of 170, about 13: if 170 had a factor bigger than that, its partner would be smaller and would already have been found.
The quick checks first
- Divisible by 2? Yes: the last digit is even.
- Divisible by 3? No: the digit sum is 8.
- Divisible by 5? Yes: the last digit is 0.
- Divisible by 9? No: the digit sum is 8.
- Divisible by 10? Yes: the last digit is 0.
All the factors of 170
1, 2, 5, 10, 17, 34, 85, 170 (8 factors)
Prime factorisation: 2 × 5 × 17.
The primes near 170
The prime before 170 is 167; the prime after it is 173.
🧮 Calculator
The answer appears here, with the working in words.
✏️ Five questions, answers hidden
1. Is 171 prime?
Answer: no
2. Is 172 prime?
Answer: no
3. What is the smallest prime factor of 174?
Answer: 2
4. List the primes between 10 and 30.
Answer: 11, 13, 17, 19, 23, 29
5. Up to which number do you need to test divisors for 511?
Answer: the square root, about 22
📚 The class this belongs to
Prime and composite numbers are taught in Grade 4 and 5 in the US, Year 5 in the UK (KS2), Class 5 and 6 in CBSE and Year 5 and 6 in Australia.
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