What's the production code of the episode written by Kirker Butler and directed by Dan Povenmire?
CREATE TABLE "table1_20613292_1" (
  "no_in_series" real,
  "no_in_season" real,
  "title" text,
  "directed_by" text,
  "written_by" text,
  "original_air_date" text,
  "production_code" text
);
SELECT "production_code" FROM "table1_20613292_1" WHERE "written_by"='Kirker Butler' AND "directed_by"='Dan Povenmire';