Update: 16th Feb It's now looking likely that this will not be episode 4.09 but will be push back a few episodes but still be part of this Season. It looks like the strike and the reduction of episodes has caused a bit of a re-think.
Just had some interesting info sent through to me. I'm trying to contact my confirmed sources to see what they have to say. I'm placing in rumours until I can clarify. Below is a summary from a much larger exchange.
1) Episode 4.9, pre-strike was going to be a Ben-Centric episode
2) The title penciled in was "The Outlier"
3) A Numbers Theory professor was brought in as a consultant by the TPTB to write a proof called "The Jacobian Code"
4) This code involved maritime calculations which were given to him, and the typical Lost numbers of 4,8,15,16,23,42. His job was to make a real proof with the maritime calculations and the Lost numbers and formulate it into an equation which as mentioned above is called the "Jacobian Code"
5) The code was to be featured in the show in episode 9 and he was told that when the code was featured in the background it would become one of televisions most tivo'd moments of all time
6) The proof is described as complex but solvable to the mildly educated math student.
Source: Jaxon