public class CubanPrimes {

    private static int MAX = 1_400_000;
    private static boolean[] primes = new boolean[MAX];

    public static void main(String[] args) {
        preCompute();
        cubanPrime(200, true);
        for ( int i = 1 ; i <= 5 ; i++ ) {
            int max = (int) Math.pow(10, i);
            System.out.printf("%,d-th cuban prime = %,d%n", max, cubanPrime(max, false));
        }
    }

    private static long cubanPrime(int n, boolean display) {
        int count = 0;
        long result = 0;
        for ( long i = 0 ; count < n ; i++ ) {
            long test = 1l + 3 * i * (i+1);
            if ( isPrime(test) ) {
                count++;
                result = test;
                if ( display ) {
                    System.out.printf("%10s%s", String.format("%,d", test), count % 10 == 0 ? "\n" : "");
                }
            }
        }
        return result;
    }

    private static boolean isPrime(long n) {
        if ( n < MAX ) {
            return primes[(int)n];
        }
        int max = (int) Math.sqrt(n);
        for ( int i = 3 ; i <= max ; i++ ) {
            if ( primes[i] && n % i == 0 ) {
                return false;
            }
        }
        return true;
    }

    private static final void preCompute() {
        //  primes
        for ( int i = 2 ; i < MAX ; i++ ) {
            primes[i] = true;
        }
        for ( int i = 2 ; i < MAX ; i++ ) {
            if ( primes[i] ) {
                for ( int j = 2*i ; j < MAX ; j += i ) {
                    primes[j] = false;
                }
            }
        }
    }
}