What's the production code of the episode written by Kirker Butler and directed by Dan Povenmire?
CREATE TABLE table_23768 (
    "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 table_23768 WHERE "Written by" = 'Kirker Butler' AND "Directed by" = 'Dan Povenmire'
Below are sql tables schemas paired with instruction that describes a task. Using valid SQLite, write a response that appropriately completes the request for the provided tables. ### Instruction: What's the production code of the episode written by Kirker Butler and directed by Dan Povenmire? ### Input: CREATE TABLE table_23768 (
    "No. in series" real,
    "No. in season" real,
    "Title" text,
    "Directed by" text,
    "Written by" text,
    "Original air date" text,
    "Production code" text
) ### Response: SELECT "Production code" FROM table_23768 WHERE "Written by" = 'Kirker Butler' AND "Directed by" = 'Dan Povenmire'