fatorial com biginteger

import java.math.BigInteger;
import java.util.HashMap;
import java.util.Map;

public class Main {
    public static void main(String[] args) {
        System.out.println(fac(0));
        System.out.println(fac(1));
        System.out.println(fac(2));
        System.out.println(fac(3));
        System.out.println(fac(5));
        System.out.println(fac(22));
    }

    public static String fac(int n) {
        Map<Integer, BigInteger> map = new HashMap<>();
        BigInteger atual = BigInteger.ONE;
        for (int i = 1; i <= n; i++) {
            atual = atual.multiply(BigInteger.valueOf(i));
            map.put(i, atual);
        }

        return atual.toString();
    }
}