What number in series was the episode written by Eric Gilliland?
CREATE TABLE "table1_27987768_1" (
  "no_in_series" real,
  "title" text,
  "directed_by" text,
  "written_by" text,
  "original_air_date" text,
  "production_code" real
);
SELECT MAX("no_in_series") FROM "table1_27987768_1" WHERE "written_by"='Eric Gilliland';