Every whole number is built from primes, like trees grow from seeds. Catch primes, grow factor trees, sift a hundred square and solve puzzles with factors and multiples!
🌲 Your forest
✨ Golden primes
PRIME FACTS
A prime number has exactly two factors: 1 and itself. 2, 3, 5, 7, 11 and 13 are primes.
1 is not a prime: it has only one factor.
2 is the only even prime. Every other even number can be divided by 2.
A number with more than two factors is composite, like 12 = 2 × 2 × 3.
Every whole number above 1 can be written as primes multiplied together in just one way (apart from the order). Whichever factor tree you grow, the leaves are the same!
The highest common factor of two numbers is the biggest number that divides both. The lowest common multiple is the smallest number both divide into.
The Sieve of Eratosthenes, from ancient Greece, finds primes by crossing out the multiples of each prime in turn.