This can be printed without raft or supports.

This is a monkey saddle surface z = (x^3-3xy^2)/2. A traditional saddle keeps one on the horse with places for both legs. This saddle has a place for two legs and a tail!

Mathematically: the shape has a flat spot right in the middle that is neither a maximum nor a minimum. However, the flat spot is even flatter than for a classical saddle.

For more information see http://gmumathmaker.blogspot.com/2015/01/monkey-saddle.html