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🔑 Prime Numbers and Prime Factorisation

Meet the special numbers that build everything!

🎯 What You'll Learn

  • Understand what makes a number prime
  • Identify prime and composite numbers
  • Use factor trees for prime factorisation
  • Apply prime knowledge to solve problems

🌟 Why It Matters

Prime numbers are the building blocks of all numbers. Prime factorisation is key in cryptography, coding, and simplifying problems.

🔍 Prime Number Detector

Enter a number to check if it's prime:

🌟 What are Prime Numbers?

Prime Number: A number that has exactly two factors - 1 and itself.


Examples:

  • 7 is prime - only factors are 1 and 7
  • 11 is prime - only factors are 1 and 11
  • 8 is NOT prime - factors are 1, 2, 4, and 8
  • 1 is NOT prime - it only has one factor (itself)

🎯 Prime Numbers from 1 to 50

Click on a number to see if it's prime!

Click on any number to learn about it!

💪 Practice Exercises

1. Is 13 a prime number?
Yes
No
2. What is the smallest prime number?
2
1
3
5
7
3. How many prime numbers are there between 10 and 20?
4
2
3
5
6

⚠️ Watch Out For These Common Mistakes!

❌ Saying 1 is prime
Wrong: 1 is the first prime number
✅ Right: 1 is neither prime nor composite (it's special)

Prime numbers need exactly TWO factors. 1 only has one factor!

❌ Forgetting that prime numbers only have two factors
Wrong: 9 is prime because 3 × 3 = 9
✅ Right: 9 is composite because it has factors 1, 3, and 9

Count ALL the factors, not just the multiplication that makes it!

❌ Thinking all odd numbers are prime
Wrong: 15 is prime because it's odd
✅ Right: 15 = 3 × 5, so it's composite

Being odd doesn't make a number prime. Check for factors!

✨ Quick Summary

Prime Power: Primes build everything. Use factor trees to break numbers down.
  • ✅ Prime definition: Exactly two factors (1 and itself)
  • ✅ First primes: 2, 3, 5, 7, 11, 13, 17, 19, 23...
  • ✅ Special cases: 1 is neither prime nor composite
  • ✅ Factor trees: Break composite numbers into prime factors
  • ✅ Real-world use: Cryptography, security, and advanced math
Remember: Prime numbers are the building blocks of all other numbers! 🔑