public static List<Integer> factorize(int n){

        List<Integer>  factors = new ArrayList();

        int i;

        boolean isPrime = true;

        for (i = 2; i <= Math.sqrt(n); i++){

            if (n % i == 0){

                factors.add(i);

                isPrime = false;

                break;

            }

        }

        if (isPrime){

            factors.add(n);

        }else{

            factors.addAll(factorize( n / i));

        }

        return factors;

    }

public static int f2(int a, int n){

        int s = 0;

        int an = 0;

        for (int i = 1; i <= n; i++){

            an += a * Math.pow(10, n-1);

            s += an;

        }

        return s;

    }

 // g = aa...a

    public static int g(int a, int n){

        if (n > 1){

            return g(a, n -1) + a * (int)Math.pow(10, n-1);

        }else if ( n == 1){

            return a;

        }else {

            throw new RuntimeException();

        }

    }

    //f = a + aa + aaa + aaaa + aa...a

    public static int f(int a, int n){

        if (n > 1){

            return f(a, n -1) + g(a,n);

        }else if ( n == 1){

            return a;

        }else {

            throw new RuntimeException();

        }

    }