#include<bits/stdc++.h>
using namespace std;
using ll = long long;
using pll = pair<ll, ll>;
#define drep(i, cc, n) for (ll i = (cc); i <= (n); ++i)
#define rep(i, n) drep(i, 0, n - 1)
#define all(a) (a).begin(), (a).end()
#define pb push_back
#define fi first
#define se second
mt19937_64 rng(chrono::system_clock::now().time_since_epoch().count());
const ll MOD1000000007 = 1000000007;
const ll MOD998244353 = 998244353;
const ll MOD[3] = {999727999, 1070777777, 1000000007};
const ll LINF = 1LL << 60LL;
const int IINF = (1 << 30) - 1;


void solve(){
	int n; cin >> n;
	vector<ll> a(n+1);
	for(int i=1; i<=n; i++) cin >> a[i];

	ll lo = -1;
	ll hi = 1e11;
	ll mid;
	while(hi-lo>1){
		mid = (lo + hi)/2;
		vector<ll> b(n+1);
		for(int i=1; i<=n; i++) b[i] = a[i] + i*mid;
		bool check = true;
		for(int i=2; i<=n; i++) if(b[i-1]>=b[i]) check = false;
		if(check) hi = mid;
		else lo = mid;
	}

	cout << hi << '\n';
}

int main(){
	cin.tie(nullptr);
	ios::sync_with_stdio(false);
	
	int T=1;
	cin >> T;
	while(T--) solve();
}