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

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

int main()
{
    long long t;
    cin >> t;
    while(t--){
        long long n;
        cin >> n;
        vector<long long> a(n);
        int flag = 0;
        for(long long i = 0; i < n; i++){
            
            cin >> a[i];
            if (i > 0 && a[i] <= a[i-1])
            {
                flag = 1;
            }
        }
        if(!flag){
            cout << 0 << endl;
        }else{

            long long low = 0;
            long long high = INT_MAX;
            long long ans = high;
            while(low <= high){
                long long mid = low + (high-low)/2;
                if(possible(a,mid)){
                    ans = high;
                    high = mid - 1;
    
                }else{
                    low = mid + 1;
                }
            }
            cout << ans << endl;
        }
    }
}