题解 | #等差数列#

const rl = require("readline").createInterface({ input: process.stdin });
var iter = rl[Symbol.asyncIterator]();
const readline = async () => (await iter.next()).value;

void async function () {
    // Write your code here
    while(line = await readline()){
        let n = parseInt(line);
        let sum = 0;
        let shulie_arr = [2]    // 数列数组，先初始化第一个元素
        for(let i=1; i<n; i++){
            shulie_arr.push(shulie_arr[i-1]+3);
        }
        for(let i=0;i<n;i++){
            sum += shulie_arr[i];
        }
        console.log(sum);
    }
}()