Naive Primality Test

Please enter a number less than 2,147,483,648 (do not use commas):
The algorithm will test it to see whether or not it is prime.

The algorithm executed here is very naive: first it sees whether 2 divides the number, then whether 3 divides it, then 5, then 7, then 9, then 11, etc. up to the square root of the number to be tested. Yes, it simply adds 2 to the trial divisor, which is a bit wasteful: for example it would check divisibility by 9 even after non-divisibility by 3 was verified. And it would check divisibility by 105 even after divisibility by 3, by 5, and by 7 were checked. On the other hand, it would be more complicated to exclude such...