Prime number

Pre knowledge
Sieve of Eratosthenes

composite number

Activity
Group by divisors e.g. number 11 is equals 2 times 4 plus three

Connecting to the web
http://mathworld.wolfram.com/PrimeNumber.html

https://www.wired.com/2013/05/twin-primes/

https://math.wikia.com/wiki/Prime_number