Unicode has code points for superscript/subscript digits. That one is U+00B9: https://www.compart.com/en/unicode/U+00B9 (So it's "normal text", as far as HN is concerned. Note that HN does filter some things, like emoji.)
I was on macOS when I typed it, there it's Control+Cmd+Space, and then search for "super" which gets close enough.
On my Linux machine, I can either do Compose, ^, 1, or Super+e and then search for it. (But both of these require configuration; either setting a key to be Compose (I sacrifice RAlt), or setting up whatever it is the IME I have is for Super+e.)
