Watch the Sieve of Eratosthenes eliminate composite numbers one by one — until only the primes are left glowing!
Start with all numbers 2–100. The first number (2) is prime — circle it, then cross out all its multiples (4, 6, 8...). Move to 3 — prime! Cross out 6, 9, 12... Keep going. Any number not yet crossed out is prime!
A prime number has exactly two factors: 1 and itself. Examples: 2, 3, 5, 7, 11, 13... A composite number has more than two factors. The number 1 is neither prime nor composite.
This free interactive math tool helps students visualize and understand mathematical concepts. Instead of memorizing procedures, students can see how numbers work through visual models, manipulatives, and step-by-step animations. Research shows that visual learning in math leads to deeper conceptual understanding.
All math tools on SmartOnlineGames are aligned with Common Core State Standards for Mathematics and are designed for students in grades K through 8. They are completely free, require no login or account creation, and work on any device including tablets, Chromebooks, and interactive whiteboards.
Interact with the visual tool above to explore the concept. Try different inputs and observe how the output changes. Teachers can use this tool for whole-class demonstrations or independent practice. Parents can use it for homework help or math enrichment at home.
Last reviewed: April 2026