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
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