from itertools import pairwise


def f(p, q, d) -> int:
    assert p > q
    return d // (p - q) + 1


def solve():
    N = int(input())
    A = list(map(int, input().split()))

    t = 0
    for i, (a, b) in enumerate(pairwise(A), 1):
        x = a + i * t
        y = b + (i+1) * t
        if y <= x:
            t += f(i+1, i, x-y)

    print(t)


T = int(input())
for _ in range(T):
    solve()