Formula for Seating Chart?

Hi All,
I work for a college where we set up a seating chart for our Board, when they meet at our school for their trimester meetings. We try not to have them sit with the same people time after time and in fact prefer no repeats within the past two meetings. I know there probably not a way to completely take care of this, but perhaps something that produces a nice outline that gets me most of the way?

I've started by assigning each of our guests a number and then assigning them a table number. So is there a way to create a logic formula (or any kind of formula) that would look to see who they sat with last time and then give them a table number that has occupants that are different from before?