题解 | #等差数列#
等差数列
https://www.nowcoder.com/practice/f792cb014ed0474fb8f53389e7d9c07f
#include <iostream>
using namespace std;
int main() {
int a, b,c;
while (cin >> a ) { // 注意 while 处理多个 case
b=2+3*(a-1);
c=(2+b)*a/2;
}
cout<<c;
}
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