Question: What is the highest number of Seats 2006 held by the communities of Bürger Für Groß-Rohrheim Party/Voter Community, with a %2006 less than 21.3?
SQL: SELECT MAX(seats_2006) FROM table_name_5 WHERE parties_and_voter_communities = "bürger für groß-rohrheim" AND _percentage_2006 < 21.3