If your paper is very short (less than 10 pages), well-written and with a fairly straightforward proof, you can try Comptes Rendus Mathematiques https://comptes-rendus.academie-sciences.fr/mathematique/. It is a reputable journal, and depending on the area there are several examples where the paper is accepted within a week (again, for that it must not require any revisions).

If your paper is longer, maybe you can extract a key lemma and submit it to that journal.