#include <iostream>
#include <vector>
#include <algorithm>
#include <climits>
using namespace std;

// vector<vector<bool>> dp
bool possible(const vector<long long> &a, long long mid)
{
    vector<long long> v = a;
    for (long long i = 0; i < v.size(); i++)
    {
        v[i] += (i + 1) * mid;
    }
    for (long long i = 1; i < v.size(); i++)
    {
        if (v[i] < v[i - 1] + 1)
            return false;
    }
    return true;
}

int main()
{
    long long t;
    cin >> t;
    while (t--)
    {
        long long n;
        cin >> n;
        vector<long long> a(n);
        for (auto &x : a)
            cin >> x;

        long long low = 0, high = 1e18, ans = 0;

        while (low <= high)
        {
            long long mid = low + (high - low) / 2;
            if (possible(a, mid))
            {
                ans = mid;
                high = mid - 1;
            }
            else
            {
                low = mid + 1;
            }
        }
        cout << ans << '\n';
    }
}