for迴圈

public class Test{
	public static int fac(int n){
	int a = 1;
	int s = 0;
	for(int i =1;i<=n;i++){
		a *= i;
		s += a;
	}
	return s;
	}
	public static void main (String[] args){
	int result = fac(3);
	System.out.println(result);
	}
}

遞迴

public class Test7{
	public static int fac(int n){
	if(n == 1){
		return 1;
	}else{
		return fac(n-1)*n;
	}
	
	}
	public static void main (String[] args){
	int result = fac(3);
	System.out.println(result);
	}
}