Sage cell server isn't giving me the output I expect

edit

This code runs fine on CoCalc:

def D(n):
    if n <= 1:
        return matrix([1])
    l = [1,-1] + [0]*(n-2)
    M = matrix(l)
    i = 1
    for _ in range(n - 1):
        l = [i] + l[:-1]
        M = M.stack(matrix(l))
        i = 0
    return M

for i in range(6):
    A = D(i)
    A
    A.det()

But when I put it in the box at http://sagecell.sagemath.org there's no output. Why could this be?