How to publish an original idea which has no citations and has been described as 'possibly notable'?
You might want to try and win over a co-author. An expert in the field can provide the needed background, the literature review you might be missing and might also be able to tell you if your paper is really worth publishing.
Maybe what you wrote is clear for every expert on the field, due to some results by someone that you simply don't know of?

Small advice here: People who are working on a PhD or just got one recently have often more time and are more willing to read something that might potentially lead to a publication than (old) professors.

Next, you might try to contact the journal you send your article to. Maybe they are able to explain the rejection?

Last but not least: If your idea is short enough to put it on Wikipedia, you might try to post it (or at least part of it) on Mathoverflow. If you follow the rules there, you might find someone who is able to tell you if this is really something "new" or if it is obvious/wrong/...