题解 | 等差数列
等差数列
https://www.nowcoder.com/practice/f792cb014ed0474fb8f53389e7d9c07f
from functools import cache import sys num = int(input()) @cache def dfs(n): if n == 1: return 2 return dfs(n-1) + 3 res = 0 for i in range(1,num+1): res += dfs(i) print(res)
斐波那契,但是这个应该是能总结出数学公式的,忘记怎么推导了