31 - 331 - 3331 - Primes - 3331 - 331 - 31

This puzzle is a little technical. It involves prime numbers. A number is a prime if its only factors are itself and one. So 6 is not a prime, as it has factors of 2 and 3. 7 is a prime. There is a little more about primes here.

This puzzle looks at the sequence 31, 331, 3331, etc and sees if each number is a prime.
Click on Next for the next number, then click on either Prime or Not Prime.