牛客网暑期ACM多校训练营（第四场）C（Chiaki Sequence Reloaded）

题目描述 Chiaki is interested in an infinite sequence a1, a2, a3, ..., which defined as follows: Chiaki would like to know the sum of the first n terms of the sequence, i.e. . As this number may be very l

>>阅读原文<<