In Brazil, we use ª for feminine ordinal numbers, just like 1st, 2nd, 3rd... in English. So it's a very common need. I just set up the Compose Key, so I can do "Compose Key, o, o" to get the masculine ordinal ° (in fact, this is the degree sign, but they're both similar. The real masculine ordinal faces the same problem as the feminine). But, although this site says I could get the ª with "Compose Key, a, _" (or similar compositions), I'm getting ā or Ā instead of ª.
Is there an easy way to type ª in Ubuntu 16.04 (LibreOffice, gedit, etc)? Please I'm not interested in memorizing/typing complex Unicode sequences.
EDIT
After the answer from Ludenticus, I realized that I can type only
Alt Gr + [ for ª
Alt Gr + ] for º
