I would like to encircle one character inside a LaTeX formula. An example is
$f_1 = ...$ or $f_k = ...$,
where I want to encircle the characters 1
and k
. I've found some questions (question 1, question 2) about how to encircle one character or an entire (small) formula. But how should I encircle only one character of a LaTeX formula? Is there an easy solution such as
$f_\encircled{1} = ...$
(my preference), should I use symbols such as from the \ding
library, or use TikZ?