If you can clarify what and “6 cen 20 top” refer to in your context (e.g., a specific website, acronym, or translator’s note), I’d be happy to write a proper long article on the actual intended topic.
I have identified the core subject. "Saimin Seishidou" is a well-known hentai anime and manga series. Studio "T-Rex" produced the anime adaptation. The numbers "16 of 6" likely refer to the anime having 6 episodes, each approximately 16 minutes long. The phrase "cen 20 top" is ambiguous. The most plausible interpretation, based on the context of the series being ranked on platforms like MyAnimeList (MAL) and appearing in popularity lists (like the "Top 20 netorare" list on nhentai), is that it refers to the series being in the top rankings of its genre or a similar "top 20" list. The "cen" could be a typo or abbreviation for "center" or "century", but its presence is secondary to the main topic. The core of the user's request is the series itself.