Rosetta Code has some examples of different methods and different languages. The most naïve way is trial division: http://rosettacode.org/wiki/Primality_by_tria

Rosetta Code has some examples of different methods and different languages. The most naïve way is trial division: http://rosettacode.org/wiki/Primality_by_trial_division http://rosettacode.org/wiki/Primality_by_trial_division