reduplication[1], in case you find that sort of thing interesting. Almost exact reduplication, bar the ending - is ending in -in or -din allowed in Brazilian Portuguese?
"N"s also can't come before "P" or "B", in which case they also get replaced by "m". This is true in Spanish as well, though the first rule isn't.
In European portuguese, while the above forms are also common, the alternatives "electrão, protão, neutrão" are often found.