CF1717E.Madoka and The Best University
普及/提高-
通过率:0%
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题目描述
Madoka wants to enter to "Novosibirsk State University", but in the entrance exam she came across a very difficult task:
Given an integer n , it is required to calculate ∑lcm(c,gcd(a,b)) , for all triples of positive integers (a,b,c) , where a+b+c=n .
In this problem gcd(x,y) denotes the greatest common divisor of x and y , and lcm(x,y) denotes the least common multiple of x and y .
Solve this problem for Madoka and help her to enter to the best university!
输入格式
The first and the only line contains a single integer n ( 3≤n≤105 ).
输出格式
Print exactly one interger — ∑lcm(c,gcd(a,b)) . Since the answer can be very large, then output it modulo 109+7 .
输入输出样例
输入#1
3
输出#1
1
输入#2
5
输出#2
11
输入#3
69228
输出#3
778304278
说明/提示
In the first example, there is only one suitable triple (1,1,1) . So the answer is lcm(1,gcd(1,1))=lcm(1,1)=1 .
In the second example, lcm(1,gcd(3,1))+lcm(1,gcd(2,2))+lcm(1,gcd(1,3))+lcm(2,gcd(2,1))+lcm(2,gcd(1,2))+lcm(3,gcd(1,1))=lcm(1,1)+lcm(1,2)+lcm(1,1)+lcm(2,1)+lcm(2,1)+lcm(3,1)=1+2+1+2+2+3=11