Prime or Not?
A fast-paced number classification game. Is the number prime or composite? Race against the clock and beat your streak!
How to Play Prime or Not?
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Choose Difficulty and Mode
Pick Easy (2–50), Medium (2–200), or Hard (2–500). Choose 60-Second Rush or Survival mode.
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A Number Appears
A number flashes on screen. Quickly decide: is it prime (divisible only by 1 and itself) or composite (has other factors)?
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Click Prime or Not Prime
Tap the 'Prime ✓' or 'Not Prime ✗' button — or press ← / P for Prime, → / N for Not Prime on keyboard. Instant feedback shows correct or wrong.
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Learn from Composites
When a number is composite, its factorization is shown (e.g. 77 = 7 × 11). Use this to build your mental library of tricky composites that look prime.
Key Features
Instant Factorization Feedback
After each answer, composite numbers reveal their factorization (e.g. '91 = 7 × 13'), turning every round into a learning moment. You'll quickly learn to recognize deceptive composites.
60-Second Rush and Survival Modes
Rush mode challenges you to classify as many numbers as possible in 60 seconds — great for building speed. Survival mode has no timer but gives you 3 lives, rewarding accuracy over pace.
Three Difficulty Ranges
Easy uses numbers 2–50, Medium 2–200, and Hard 2–500. Larger numbers require mental trial division — is 437 prime? (No, 19 × 23.) — demanding real number theory knowledge.
Streak Tracker with Milestones
Track your consecutive correct streak with milestone celebrations at 5, 10, 25, and 50 in a row. Breaking a long streak is genuinely painful — in the best possible way.
What is Prime or Not?
Prime or Not? is a speed-classification game that trains your ability to quickly identify prime numbers. A prime number is divisible only by 1 and itself — 2, 3, 5, 7, 11, 13... A composite number has other divisors — 4, 6, 9, 10, 15, 21... The game builds both your knowledge of specific primes and composites, and your mental strategies for quick trial division. Hard mode with numbers up to 500 is genuinely challenging — numbers like 491 (prime) and 493 (= 17 × 29) require systematic reasoning.
Why Play Prime or Not?
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Builds Prime Number Intuition
After enough rounds, you'll have many primes and deceptive composites committed to memory — invaluable for factoring problems, GCD/LCM calculations, and number theory.
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Reinforces Divisibility Rules
Playing regularly sharpens your divisibility rules: divisible by 2 (even), by 3 (digit sum divisible by 3), by 7 (no simple rule but you get faster). These rules speed up all arithmetic.
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Perfect for Math Competition Prep
AMC, MATHCOUNTS, and similar competitions frequently involve prime factorization and prime recognition. This game builds the fluency needed to solve those problems quickly.
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Eye-Opening for Beginners
Many people are surprised to discover that 91 = 7×13 (not prime!) and 97 is prime. The factorization feedback after each composite builds genuine number theory knowledge.
Frequently Asked Questions
Is 1 considered a prime number in this game?
No — 1 is neither prime nor composite by mathematical convention. By definition, prime numbers have exactly two distinct positive divisors (1 and themselves), while 1 has only one divisor. The game starts from 2.
What's the hardest part about large numbers?
Numbers that look prime but aren't — like 91 (7×13), 119 (7×17), 143 (11×13), 221 (13×17), and 323 (17×19). These require checking divisibility by primes beyond the obvious 2, 3, 5, and 7. Hard mode includes many such 'impostor composites'.
What keyboard shortcuts are available?
Press ← arrow or 'P' for Prime; → arrow or 'N' for Not Prime. Enter advances after feedback. These shortcuts allow extremely fast play in 60-Second Rush mode without touching the mouse.
How do you quickly check if a number is prime?
You only need to test divisibility by primes up to √n. For numbers up to 500, that means checking 2, 3, 5, 7, 11, 13, 17, 19 (since 23² = 529 > 500). If none divide evenly, the number is prime.
What accuracy grade do I need to see 'Amazing'?
You receive an 'Amazing' grade for 95%+ accuracy, 'Great' for 80–94%, 'Good' for 65–79%, and 'Keep Practicing' below that. In Rush mode, the grade is shown on the results screen along with total correct and your best streak.