dc, 3 unique bytes, 138 bytes
This challenge is pretty easy if you aim for just 4 unique bytes. For example, you could push the stack depth repeatedly to get ascending integers, set the precision ...
dc, 9 bytes
_?dvd*-^p
Try it online!
Comparisons are expensive in dc, so you have to get a bit creative. I came up with $0^{n-\lfloor\sqrt{n}\rfloor^2}$.