题解 | #等差数列#
等差数列
https://www.nowcoder.com/practice/f792cb014ed0474fb8f53389e7d9c07f
#include <stdio.h> int main() { int n=0; while(scanf("%d",&n)!=EOF) { int a=2; if(1==n) { printf("%d\n",a); } else { printf("%d\n",n*a+((n-1)*n*3)/2); } } return 0; }