user: Question: What artist's song was performed in the week with theme of Billboard #1?
Columns: ['Week', 'Theme', 'Artist', 'Order sung', 'Status']
Types: ['text', 'text', 'text', 'text', 'text']
Sample row: ['Top 24 (12 Men)', "Contestant's Choice", 'Richard Marx', '3', 'Advanced']
SQL:

assistant: SELECT "Artist" FROM "Table" WHERE "Theme" = 'Billboard #1';