#include <iostream>
#include <vector>
#include <algorithm>
#include <array>
#include <iterator>
#include <string>
#include <cctype>
#include <cstring>
#include <cstdlib>
#include <cassert>
#include <cmath>
#include <ctime>
#include <iomanip>
#include <numeric>
#include <stack>
#include <queue>
#include <map>
#include <unordered_map>
#include <set>
#include <unordered_set>
#include <bitset>
#include <random>
#include <utility>
#include <functional>
using namespace std;
void Main()
{
	int N;
	cin >> N;
	vector<int> A(N);
	for(int i = 0;i < N;i++)
	{
		cin >> A[i];
	}
	long long ng = -1,ok = (long long)2e13;
	while(ok - ng > 1)
	{
		long long mid = (ok + ng) / 2;
		vector<long long> B(N);
		for(int i = 0;i < N;i++)
		{
			B[i] = A[i] + (i + 1) * mid;
		}
		bool check = true;
		for(int i = 1;i < N;i++)
		{
			if(B[i] <= B[i - 1])
			{
				check = false;
				break;
			}
		}
		if(check)
		{
			ok = mid;
		}
		else
		{
			ng = mid;
		}
	}
	cout << ok << "\n";
}
int main()
{
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	int tt = 1;
	cin >> tt;
	while(tt--) Main();
}