#include<iostream>
using namespace std;

// GNU = GNU's Not Unix
// This sentence is false

void print_hi(){
	cout << "hi\n";
	print_hi();
}	

/*
 * 1! = 1
 * 2! = 1 * 2 = 2
 * 3! = 1 * 2 * 3 = 6
 * 4! = 1 * 2 * 3 * 4 = 24
 * 5! = 1 * 2 * 3 * 4 * 5 = 120
 * 6! = 5! * 6 = 720 
 * ... and so on
 * In general:
 * n! = (n-1)! * n
 *
 */

unsigned long int factorial(unsigned long int n){
	if(n == 1)
		return 1;
	return factorial(n - 1) * n;
}


int main(){
	cout << "6! = " << factorial(6) << endl;
	for(int i = 1; i < 21; i++){
		cout << "i" << "!: " << factorial(i) << endl;
	}
	return 0;
}