The GCD function

3.5

52 votes
Mathematics, GCD, Math, Number Theory
Problem

You are given an integer \(N\) and there is a function \(F(N)=\sum_{i=1}^{N} GCD(X,i)\). Here, GCD denotes the greatest common divisor. You are required to select an integer value \(X\) that is greater than or equal to 1

Your task is to determine the following:

  • The maximum possible value of \(F(N)\) that you can get 
  • The minimum \(X\) for which maximum value will be achieved

Input format

  • The first line contains an integer \(T\) denoting the number of test cases.
  • Next \(T\) lines contain a single integer \(N\).

Output format

Print \(T\) lines. For each test case:

  • Print a single line containing two integers, the maximum value of \(F(N)\) and the minimum value of \(X\) for which \(F(N)\) is maximized.

Constraints

\(1 \leq T \leq 40\)

\(1 \leq N \leq 40\)

Time Limit: 1
Memory Limit: 256
Source Limit:
Explanation

N is 3 so F(3)=GCD(1,x)+GCD(2,x)+GCD(x,3)

If we choose x=6 we will get F(3)=GCD(1,6)+GCD(2,6)+GCD(3,6)=6.

There is no smaller value than X=6 for which F(3)=6. Also no other value of X we can get a greater value of F(3).

 

Editor Image

?