[JorgeGT]

You can send it to a journal as a private individual, but probably a better way would to post a manuscript on arxiv.org, and once it generates certain buzz (if the problem is interesting and well solved) then either submit it to a journal yourself or partner with other mathematician to polish it, etc. and then submit.

[whitecream]

To be able to submit to arXiv, one needs to be endorsed by someone in the domain, which could be a potential hurdle for someone not in academia. (and I'm not about to suggest viXra as a way to get around that)

[Grue3]

Yeah, I actually used to be a math post-graduate and have a draft of a paper with an interesting result, so I wanted to publish it but I had no idea how to get "endorsed". This was like 10 years ago and I switched to a career in programming so I doubt I'll even understand my own proof now.