31st, etc. are the correct options. When you use ordinal numbers ending in 1, you use first. The only exception is eleventh, because although it ends in 1 its “name” doesn’t contain the word “one” like 21, 31, etc. More @Wikipedia
Hover over any link to get a description of the article. Please note that search keywords are sometimes hidden within the full article and don't appear in the description or title.