mobius: function [n][
    if n=0 -> return ""
    if n=1 -> return 1
    f: factors.prime n

    if f <> unique f -> return 0
    switch odd? size f -> return neg 1
                       -> return 1
]

loop split.every:20 map 0..199 => mobius 'a ->
    print map a => [pad to :string & 3]