Main(require("fs").readFileSync("/dev/stdin", "utf8").split("\n"));

function Main(lines) {
    const T = parseInt(lines[0]);
    for(let i=0; i<T; ++i) {
        const N = parseInt(lines[i*2+1]);
        const A = lines[i*2+2].split(" ").map(Number);

        // (l, r]
        let l = -1;
        let r = 1000000000;
        while(r-l>1) {
            let m = Math.floor((l+r)/2);
            let pre = -1;
            let ok = true;
            for(let i=0; i<N; ++i) {
                let cur = A[i] + m * (i+1);
                if(pre>=cur) {
                    ok = false;
                    break;
                }
                pre = cur;
            }
            if(ok) {
                r = m;
            } else {
                l = m;
            }
        }
        console.log(r);
    }
}