I am interested about where a mathematical discovery can be posted to be credited for it, if its "father" is an undergraduate or someone who never took mathematics courses but studies mathematics on his own and is pretty good at it? Is it some scientific company or some university?
A possible venue for unpublished articles by undergraduates or anyone else is the arxiv: https://arxiv.org/
However, you will have to get an endorsement from someone who already has an authorisation to place papers there, such as a mathematician familiar with this work. This may be nontrivial but certainly easier than getting the article published in a peer-reviewed journal.
I did original research as an undergraduate and wrote a paper on it. I published the paper I wrote on arXiv, and am currently in the process of working to get it published in a journal. In the meanwhile it's been read at least a few times because it's been cited in further work on the topic. There are also journals that specifically publish the work of undergraduates.