P6.4

public class P64 {
    public static void main(String[] args) {
        int N = Integer.parseInt(args[0]);

        boolean[] isPrime = new boolean[N + 1];
        for (int i = 2; i <= N; i++) {
            isPrime[i] = true}

        for (int i = 2; i*i <= N; i++) {

            if (isPrime[i]) {
                for (int j = i; i*j <= N; j++) {
                    isPrime[i*j] = false;}
            }
        }

        int primes = 0;
        for (int i = 2; i <= N; i++) {
            if (isPrime[i]){ primes++; System.out.print(i+", ");}
        }
        System.out.println("\nThe number of primes <= " + N + " is " + primes);
    }
}