Is 8 a prime number?
8 is not a prime number, because it is divisible by 2: 8 = 2^3, and it has 4 factors.
Checking 8 for primality, divisor by divisor
| Try | Into | Gives | Verdict |
|---|---|---|---|
| 2 | 8 | 4 remainder 0 | divides exactly |
You only need to test primes up to the square root of 8, about 2: if 8 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? No: the last digit is 8.
- Divisible by 9? No: the digit sum is 8.
- Divisible by 10? No: the last digit is 8.
All the factors of 8
1, 2, 4, 8 (4 factors)
Prime factorisation: 23.
The primes near 8
The prime before 8 is 7; the prime after it is 11.
🧮 Calculator
The answer appears here, with the working in words.
✏️ Five questions, answers hidden
1. Is 9 prime?
Answer: no
2. Is 10 prime?
Answer: no
3. What is the smallest prime factor of 12?
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 25?
Answer: the square root, about 5
📚 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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