Is 1 a prime number?
1 is not a prime number. Here is why, in plain words.
The answer
No. A prime number has exactly two different factors, and 1 has only one, so 1 is not prime.
Why 1 is not prime
A prime number has exactly two different factors: 1 and the number itself. 7 is prime because its factors are 1 and 7. 1 has only one factor, 1, so it does not pass the test.
Prime, composite or neither
| Kind of number | How many factors | Examples |
|---|---|---|
| Neither | 1 | 1 |
| Prime | Exactly 2 | 2, 3, 5, 7, 11 |
| Composite | 3 or more | 4, 6, 8, 9, 10 |
Related pages
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Questions parents ask
Is 1 a composite number?
No. A composite number has more than two factors, and 1 has only one. 1 is neither prime nor composite.
Why is 1 not counted as prime?
If 1 were prime, numbers could be split into primes in endless ways: 6 = 2 × 3 = 1 × 2 × 3 = 1 × 1 × 2 × 3. Leaving 1 out means every whole number above 1 has exactly one prime factorisation.
What is the smallest prime number?
2. It is also the only even prime number.
Continue your number practice
Explore the diagnostic for another set of practice questions.