#include <bits/stdc++.h>
using namespace std;
using ll = long long;

template<class T> istream& operator >> (istream& is, vector<T>& vec) {
    for(T& x : vec) is >> x;
    return is;
}

int main(){
    ios::sync_with_stdio(false);
    cin.tie(0);
    int T;
    cin >> T;
    while(T--){
        int n;
        cin >> n;
        vector<int> a(n);
        cin >> a;
        ll ng = -1, ok = 1'000'000'001, mid;
        while(ng + 1 < ok){
            mid = (ng + ok) / 2;
            bool flg = true;
            ll mx = -1;
            for(int i = 0; i < n; i++){
                ll v = a[i] + (i + 1) * mid;
                if(v <= mx){
                    flg = false;
                    break;
                }
                mx = v;
            }
            (flg ? ok : ng) = mid;
        }
        cout << ok << '\n';
    }
}