C :

#include<stdio.h>
int sl(int n){
	if(n==1){
	return 1;}else if(n==2){
		return 2;
	}
	else{
		return sl(n-1)*2-sl(n-2)+1;
} 
}
int main()
{
	int n,i,s=0;
	scanf("%d",&n);
	for(i=1;i<=n;i++){
		s=s+sl(i);
	}
	printf("%d",s);
return 0;
}

C++ :

#include <iostream>
#include <cmath>
using namespace std;
int num(int n){
	int r;
	if(n==1){
		r=1;
	}else{
		r=num(n-1)+n-1;
	}	
	
	return r;
}
int main(){
	int n,i,s;
	s=0;
	cin>>n;
	for(i=1;i<=n;i++){
		s=s+num(i);
	}
	cout<<s<<endl;
}

Python :

def shu(n):
    r = 0;
    if n == 1:
       r = 1;
    else:
       r = shu(n - 1) + n - 1 
    return r;

n = int(input())
s = 0
for i in range(1, n+1):
    s += shu(i)
print(s)