Is 5 a prime number?
5 is a prime number, because nothing up to its square root (about 2) divides it, so its only factors are 1 and 5.
Checking 5 for primality, divisor by divisor
| Try | Into | Gives | Verdict |
|---|---|---|---|
| 2 | 5 | 2 remainder 1 | no |
You only need to test primes up to the square root of 5, about 2: if 5 had a factor bigger than that, its partner would be smaller and would already have been found.
The quick checks first
- Divisible by 2? No: the last digit is odd.
- Divisible by 3? No: the digit sum is 5.
- Divisible by 5? Yes: the last digit is 5.
- Divisible by 9? No: the digit sum is 5.
- Divisible by 10? No: the last digit is 5.
All the factors of 5
1, 5 (2 factors)
The primes near 5
The prime before 5 is 3; the prime after it is 7. 5 and 7 are twin primes.
🧮 Calculator
The answer appears here, with the working in words.
✏️ Five questions, answers hidden
1. Is 6 prime?
Answer: no
2. Is 7 prime?
Answer: yes
3. What is the smallest prime factor of 9?
Answer: 3
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 16?
Answer: the square root, about 4
📚 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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