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

//* ATCODER
#include<atcoder/all>
using namespace atcoder;
typedef modint998244353 mint;
//*/

/* BOOST MULTIPRECISION
#include<boost/multiprecision/cpp_int.hpp>
using namespace boost::multiprecision;
//*/

typedef long long ll;

#define rep(i, s, n) for (int i = (int)(s); i < (int)(n); i++)
#define rrep(i, s, n) for (int i = (int)(n)-1; i >= (int)(s); i--)

template <typename T> bool chmin(T &a, const T &b) {
	if (a <= b) return false;
	a = b;
	return true;
}

template <typename T> bool chmax(T &a, const T &b) {
	if (a >= b) return false;
	a = b;
	return true;
}

template <typename T> T max(vector<T> &a){
	assert(!a.empty());
	T ret = a[0];
	for (int i=0; i<(int)a.size(); i++) chmax(ret, a[i]);
	return ret;
}

template <typename T> T min(vector<T> &a){
	assert(!a.empty());
	T ret = a[0];
	for (int i=0; i<(int)a.size(); i++) chmin(ret, a[i]);
	return ret;
}

template <typename T> T sum(vector<T> &a){
	T ret = 0;
	for (int i=0; i<(int)a.size(); i++) ret += a[i];
	return ret;
}

void solve(){
	int n; cin >> n;
	vector<ll> a(n);
	rep(i,0,n) cin >> a[i];

	auto check = [&](ll t) -> bool {
		vector<ll> x(n);
		rep(i,0,n){
			x[i] = a[i] + t * (i + 1);
		}
		rep(i,0,n-1){
			if (x[i] >= x[i+1]) return false;
		}
		return true;
	};

	ll ub = 4e9;
	ll lb = -1;
	while(ub - lb > 1){
		ll t = (ub + lb) / 2;
		if (check(t)) ub = t;
		else lb = t;
	}
	cout << ub << '\n';
}

int main(){
	ios_base::sync_with_stdio(false);
	cin.tie(NULL);
	int t; cin >> t;
	while(t--) solve();
}