CREATE TABLE table_20613292_1 (production_code VARCHAR, written_by VARCHAR, directed_by VARCHAR)

What's the production code of the episode written by Kirker Butler and directed by Dan Povenmire?
SELECT production_code FROM table_20613292_1 WHERE written_by = "Kirker Butler" AND directed_by = "Dan Povenmire"
SELECT "production_code" FROM "table_20613292_1" WHERE "Dan Povenmire" = "directed_by" AND "Kirker Butler" = "written_by"