What is the most effective prime no. program?

Answer 1

You can find some ideas in my code.
It is not the best, but use some technique to reduce the checks.
Try to divide until the square of the number and divide only for prime numbers.

See createPrimeList method in
https://code.sololearn.com/cnBDO3pmRV7U/#java

I hope my code can help you.

Answer 2

Some ideas here
https://stackoverflow.com/questions/622/most-efficient-code-for-the-first-10000-prime-numbers