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
More numbers
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.
Number facts are the base of 11+ maths
Factors, multiples, primes and square numbers come up all over 11+ maths, from simplifying fractions to ratio. The free diagnostic checks maths, English and both kinds of reasoning, and shows what to practise next. No card is required.