CF776E.The Holmes Children
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通过率:0%
时间限制:2.00s
内存限制:256MB
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题目描述
The Holmes children are fighting over who amongst them is the cleverest.
Mycroft asked Sherlock and Eurus to find value of f(n), where f(1) = 1 and for n ≥ 2, f(n) is the number of distinct ordered positive integer pairs (x, y) that satisfy x + y = n and gcd(x, y) = 1. The integer gcd(a, b) is the greatest common divisor of a and b.
Sherlock said that solving this was child's play and asked Mycroft to instead get the value of
. Summation is done over all positive integers d that divide n.
Eurus was quietly observing all this and finally came up with her problem to astonish both Sherlock and Mycroft.
She defined a k-composite function F__k(n) recursively as follows:

She wants them to tell the value of F__k(n) modulo 1000000007.
福尔摩斯家的孩子们正在争论,他们之中究竟谁最聪明。
迈克罗夫特让夏洛克和欧洛斯计算函数 $ f(n) $ 的值,其中 $ f(1) = 1 $,而对于 $ n \geq 2 , f(n) $ 表示满足 $ x + y = n $ 且 $ \gcd(x, y) = 1 $ 的互异的有序正整数对 $ (x, y) $ 的个数。此处 $ \gcd(a, b) $ 表示 $ a $ 与 $ b $ 的最大公约数。
夏洛克称这道题小菜一碟,于是请迈克罗夫特改为计算
的值。该求和遍历所有能整除 $ n $ 的正整数 $ d $。
欧洛斯一直安静地旁观这一切,最后提出了她自己的问题,以令夏洛克和迈克罗夫特都大为惊叹。
她递归地定义了一个 $ k $-复合函数 $ F_k(n) $,如下所示:

她要求他们计算 $ F_k(n) $ 对 $ 1000000007 $ 取模的结果。
输入格式
A single line of input contains two space separated integers n (1 ≤ n ≤ 1012) and k (1 ≤ k ≤ 1012) indicating that Eurus asks Sherlock and Mycroft to find the value of F__k(n) modulo 1000000007.
一行输入包含两个以空格分隔的整数 n(1 ≤ n ≤ 1012)和 k(1 ≤ k ≤ 1012),表示 Eurus 要求 Sherlock 和 Mycroft 计算 Fk(n) 对 1000000007 取模的值。
输出格式
Output a single integer — the value of F__k(n) modulo 1000000007.
输出一个整数——Fk(n) 对 1000000007 取模的结果。
输入输出样例
输入#1
7 1
输出#1
6
输入#2
10 2
输出#2
4
说明/提示
In the first case, there are 6 distinct ordered pairs (1, 6), (2, 5), (3, 4), (4, 3), (5, 2) and (6, 1) satisfying x + y = 7 and gcd(x, y) = 1. Hence, f(7) = 6. So, _F_1(7) = f(g(7)) = f(f(7) + f(1)) = f(6 + 1) = f(7) = 6.
第一种情况中,有 6 个互不相同的有序对 (1,6)、(2,5)、(3,4)、(4,3)、(5,2) 和 (6,1) 满足 x+y=7 且 gcd(x,y)=1。因此,f(7)=6。于是,F1(7)=f(g(7))=f(f(7)+f(1))=f(6+1)=f(7)=6。
输入解题思路,AI测评打分。不知道怎么写?