I've never seen a math journal that requires academic credentials or affiliation to submit a paper, and I've published several math papers without an academic affiliation. You can put your employer as your affiliation or even "Independent Researcher". The hard part is writing the papers themselves. Getting a paper in a decent math journal as an outsider is rare, not because the journals ban or are biased against outsiders, but just because it's rare for an outsider to write a decent math paper.