Explore prime numbers on number grids. There is no timer.
Prime hunt: mark all 25 primes from 1 to 100, then Check. Tap a marked number again to remove it.
Card investigation: choose a range, then classify each drawn number as Prime or Not prime. A prime has exactly two positive factors. 1 is not prime and is neither prime nor composite. Correct a wrong answer before pressing Next card. Each number is drawn once. The grid shows primes in yellow and composites in blue-grey; 1 has its own dashed outline. Finish ends the deck.
Odd or even?: mark every even prime. Discuss what you notice about the other primes.
Prime sums: choose two primes, enter their sum and choose Prime or Composite. To add a prime to itself, select it and press Use twice. Check three different pairs, including both a prime and a composite sum.
Prime gaps: choose two successive primes and enter their difference. Check three different pairs with at least two different gap sizes.
Hint offers a way to think. Reveal shows an answer without earning a checked example or checked-card credit. Keep exploring different examples.
Clear removes your current response and keeps checked examples. In Card investigation it keeps the drawn card and all recorded decisions. Changing the card range starts a fresh shuffled deck. Changing investigation opens a fresh response. Restart clears all progress and reshuffles the current range. It keeps the current investigation, or returns to Prime hunt when opened from Curriculum.
Use arrow keys to move around the square and Enter or Space to mark a number. Tab moves between the square and controls.
Print prints the current display on one side of A4 landscape.
