Problem Description Chiaki is interested in an infinite sequence a1,a2,a3,..., which is defined as follows: an={1an−an−1+an−1−an−2n=1,2n≥3 Chiaki would like to know the sum of the first n terms of the sequence, i.e. ∑i=1nai. As this number may be ver…
题目链接 Problem Description Chiaki is interested in an infinite sequence $$$a_1,a_2,a_3,...,$$$ which is defined as follows: $$$a_n= \begin{cases} 1, & \text{$$$n=1,2$$$} \\ a_{n-a_{n-1}}+a_{n-1-a_{n-2}} & \text{$$$n\ge 3$$$} \end{cases}$$$ Chiaki wo…
题目链接 : http://acm.hdu.edu.cn/showproblem.php?pid=6304 多校contest1 Problem Description Chiaki is interested in an infinite sequence a1,a2,a3,..., which is defined as follows: an={1an−an−1+an−1−an−2n=1,2n≥3 Chiaki would like to know the sum of the fir…
Long long ago, there is a sequence A with length n. All numbers in this sequence is no smaller than 1 and no bigger than n, and all numbers are different in this sequence. Please calculate how many quad (a,b,c,d) satisfy: 1. 1≤a<b<c<d≤n1≤a<b&l…
