prime generator

Main.java

public class Main {
   public static void main(String[] args){

      long startedAt = System.nanoTime();
      HashSet<Long> primes = new HashSet<>();
      primes.add(2L);

      for(long i = 1; i < 10000000; i+= 2) {
         boolean isPrime = true;
         for (int j = 3; j < Math.sqrt(i); j++) {
            if (i % j == 0) {
               isPrime = false;
               break;
            }
         }
         if (isPrime) {
            primes.add(i);
         }
      }
      long endedAt = System.nanoTime();

      System.out.println(primes.size());

      System.out.println("Took " + ((endedAt - startedAt) / 1000000 ));
   }
}