What was the production code of the episode written by Brendan Cowell?
CREATE TABLE "table1_25390694_2" (
  "series_num" real,
  "title" text,
  "director" text,
  "writer" text,
  "air_date" text,
  "production_code" real
);
SELECT "production_code" FROM "table1_25390694_2" WHERE "writer"='Brendan Cowell';