write a go solution for Description:
You are given an array a of n integers. Count the number of pairs of indices (i,j) such that i<j and a_j-a_i=j-i.

Input Format:
The first line contains one integer t (1<=t<=10^4). Then t test cases follow.

The first line of each test case contains one integer n (1<=n<=2*10^5).

The second line of each test case contains n integers a_1,a_2,ldots,a_n (1<=a_i<=n) — array a.

It is guaranteed that the sum of n over all test cases does not exceed 2*10^5.

Output Format:
For each test case output the number of pairs of indices (i,j) such that i<j and a_j-a_i=j-i.

Note:
None. Output only the code with no comments, explanation, or additional text.