public static boolean isPrime(int x) {
        if(x < 2)
            return false;
        for(int i = 2; i * i <= x; i++)
            if(x % i == 0)
                return false;
        return true;
    }

    public static int nextBiggerPow2(int x) {
        int p2 = 1;
        while(p2 <= x)
            p2 *= 2;
        return p2;
    }

    public static String isMersennePrime(int x) {
        if(x <= 0)
            return "Error!";

        if(isPrime(x) && nextBiggerPow2(x) - 1 == x)
            return "Yes";
        return "No";
    }