This is a very inefficient algorithm. What you are doing is counting all the divisors of a number (with the exception of divisors divisible by 5) and call it a prime if there are just 2 divisors (special casing a few numbers).

It's of course a lot more efficient to decide a number is prime as soon as you have found a divisor > 1 and smaller or equal to sqrt (number). No need to do millions of divisions to decide 100000000 is prime after finding out it's divisible by 2.

Abigail