Twin Prime Calculator
Press the green flag and it will calculate twin primes for as long as you can be bothered to watch it (or for as long as Scratch has the processing power to continue running). If it has been running for a while and has slowed down, press space to speed it up.
This can calculate 121 pairs of twin primes in just one minute.
A twin prime (or a pair of twin primes) is where two primes, for example
3 and 5, have a difference of exactly 2. There is a conjecture that there are infinite twin primes but I don't think Scratch has the processing power to calculate any more than 1000000 twin primes.