题目描述:
sum=2+5+8+11+14+…,输入正整数n,求sum的前n项和。
输入:
输出:
样例输入
2
样例输出
7
#include "stdio.h"
unsigned int n;
int main(void)
{
unsigned int sum,base;
n=0;sum=2;base=2;
scanf("%d",&n);
while(n-1)
{
base += 3;
sum = sum+base;
n--;
}
printf("%d",sum);
return 0;
}