The fanfiction "The Pervetiest Central Finite Curve" is a piece of adult-oriented Rick and Morty fanfiction likely hosted on platforms like Literotica or Archive of Our Own (AO3). You can try finding this text by searching directly on these sites or by using specialized search queries.
Regarding the official show, the Central Finite Curve is a barrier created by Rick C-137 to isolate universes where he is the smartest person. It was built by the Citadel to ensure Rick's dominance across the multiverse and to assist in finding Rick Prime. RickAndMorty-ThePervetiestCentralFiniteCurve-CH...