#include<stdio.h>
#include<stdlib.h>
int main()
{ system("color 3E");
int i=1,j=1,n;
long sum=0,s=0;
printf("输入项数N\n");
scanf("%d",&n);
if(n<1)
{printf("the n must be no less than 1!\n");
return 0;}
for(;i<=n;i++)
{
for(;j<=i;j++)
{
s=s+i;
}
sum=sum+s;
}
printf("the sum of the sequence %d is %ld\n",n,sum);
return 0;
}
