Prime Numbers
⭐ MasteredA prime number can only be divided evenly by 1 and itself. 2, 3, 5, 7 and 11 are primes.
2 is the only even prime number.
All about Prime Numbers
A prime number is a whole number greater than 1 that has exactly two factors: 1 and itself. The first few primes are 2, 3, 5, 7, 11, 13 and 17. Numbers with more than two factors are called composite numbers.
For example, 9 is composite because it can be divided by 3. Prime numbers are used in computer codes that keep information safe online.
🎮 Try it yourself!
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👀 What the animation shows
This animation shows a number of objects being arranged into rectangles. Watch how a prime number can only make one rectangle in a single row, while other numbers can be arranged in more ways.
Real-life uses of Prime Numbers
- Keeping secret codes safe, because computers use very large primes for encryption
- Splitting a group into equal teams only when the number is not prime
- Solving puzzles and number games
Frequently asked questions about Prime Numbers
Is 1 a prime number?
No. A prime needs exactly two different factors, and 1 has only one.
What is the biggest known prime?
Mathematicians keep finding larger primes using computers. The largest known prime has millions of digits.
How can you tell if a number is prime?
Check whether any number from 2 up to its square root divides into it exactly. If none does, it is prime.