C++ :

#include<cstdio>
using namespace std;
int main()
{
	int n;
	scanf("%d",&n);
	int a[n+1];
	a[1]=2;
	for(int i=2;i<=n;++i)
	a[i]=a[i-1]+i;
	printf("%d",a[n]);
	return 0;
}

Pascal :

program hjc;
var
 f:array[1..1000] of integer;
 n,i:integer;

begin
 f[1]:=2;
 readln(n);
 for i:=2 to n do
  begin
   f[i]:=f[i-1]+i;
  end;
  writeln(f[n]);
end.