题解 | #等差数列#
等差数列
https://www.nowcoder.com/practice/f792cb014ed0474fb8f53389e7d9c07f
#include <iostream>
using namespace std;
int main() {
int n;
cin >> n;
int a = 2; //首项
int sum = 2; //求和
for (int i = 1;i < n;i++)
{
a += 3;
sum += a;
}
cout << sum;
}
// 64 位输出请用 printf("%lld")
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