Is 7 a prime number?
7 is a prime number, because nothing up to its square root (about 2) divides it, so its only factors are 1 and 7.
Checking 7 for primality, divisor by divisor
| Try | Into | Gives | Verdict |
|---|---|---|---|
| 2 | 7 | 3 remainder 1 | no |
You only need to test primes up to the square root of 7, about 2: if 7 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 7.
- Divisible by 5? No: the last digit is 7.
- Divisible by 9? No: the digit sum is 7.
- Divisible by 10? No: the last digit is 7.
All the factors of 7
1, 7 (2 factors)
The primes near 7
The prime before 7 is 5; the prime after it is 11.
🧮 Calculator
The answer appears here, with the working in words.
✏️ Five questions, answers hidden
1. Is 8 prime?
Answer: no
2. Is 9 prime?
Answer: no
3. What is the smallest prime factor of 11?
Answer: 11
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 22?
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.
If this page is the homework and the method is not sticking, that is what a 1-on-1 class fixes: one tutor with a master's degree, one child, on a shared whiteboard, in your time zone, about US$10 to $13 an hour. How 1-on-1 online tutoring works.