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Primes in Space

Feed Septimus the Space Monster primes, and primes alone! Click on numbers that are not prime to stop them from reaching him, for they are poison to him. If you click on a prime number, you are forced to return to earth as the Space Monster goes into a rage. See how far you can go. As time goes on, the numbers get larger and more difficult to factor, arrive more quickly, and move more quickly across the screen. Players with a score over 100 beware!

If you can achieve a score of 120 or above, post a video of your feat on YouTube and we will include you and your video on a leaderboard on our site. Let us know at

Credit where Credit is Due

big primes