const INF: u128 = 1u128 << 60;

fn main() {
    let mut t = String::new();
    std::io::stdin().read_line(&mut t).ok();
    let t: usize = t.trim().parse().unwrap();
    for _ in 0..t {
        let mut n = String::new();
        std::io::stdin().read_line(&mut n).ok();
        let n: usize = n.trim().parse().unwrap();
        let mut a = String::new();
        std::io::stdin().read_line(&mut a).ok();
        let a: Vec<u128> = a.trim().split_whitespace().map(|s| s.parse().unwrap()).collect();

        let mut lower = 0u128;
        let mut upper = INF;
        while upper > lower {
            let middle = (upper + lower) / 2;
            let next_a = (0..n).map(|i| a[i] + (i as u128 + 1) * middle).collect::<Vec<_>>();
            if next_a.windows(2).all(|lr| lr[0] < lr[1]) {
                upper = middle;
            } else {
                lower = middle + 1;
            }
        }
        println!("{}", upper);
    }
}