user: Question: What is the production code of the episode that was watched by 3.81 million U.S. viewers? 
Columns: ['No. in series', 'Title', 'Directed by', 'Written by', 'Original air date', 'Production code', 'U.S. viewers (million)']
Types: ['real', 'text', 'text', 'text', 'text', 'text', 'text']
Sample row: [1.0, '" Pilot "', 'Marcos Siega', 'Teleplay by: Kevin Williamson & Julie Plec', 'September10,2009', '296766', '4.91']
SQL:

assistant: SELECT "Production code" FROM "Table" WHERE "U.S. viewers (million)" = '3.81';