What is the production code of the episode written by Jeff Filgo?
CREATE TABLE "table1_27988281_1" (
  "no_in_series" real,
  "no_in_season" real,
  "title" text,
  "directed_by" text,
  "written_by" text,
  "original_air_date" text,
  "production_code" real
);
SELECT MAX("production_code") FROM "table1_27988281_1" WHERE "written_by"='Jeff Filgo';