My code is as follows.
textView.setText(Html.fromHtml("6<sup>4</sup>"));
The output is:

Now I want to change the size of 4, so I applied the font as follows, but font is not getting applied.
textView.setText(Html.fromHtml("6<sup><font size="-2">4</font></sup>"));
How do I fix this problem?
According to android.text.Html (on GrepCode), you may use
<small>for smaller text, as<font>only supports color and face attributes.