BigInteger Recursive Combination Method

Hello guys, This post will be small. I just encounter a problem where I need to find combination of a number and results would be big that cannot be even stored in long, so a BigInteger is required. Here is the code:

private static BigInteger factorial(int N) {
        if(N == 1) {
            return BigInteger.valueOf(1);
        }       
        return BigInteger.valueOf(N).multiply(factorial(N-1));
}