import java.util.BitSet; public class HundredDoors { public static void main(String[] args) { final int n = 100; var a = new BitSet(n); for (int i = 1; i <= n; i++) { for (int j = i - 1; j < n; j += i) { a.flip(j); } } a.stream().map(i -> i + 1).forEachOrdered(System.out::println); } }