user: Question: What is the whenbuilt of the Brighton built Blandford Forum with a withdrawn of September 1964?
Columns: ['BRNo.', 'Name', 'Builder', 'Whenbuilt', 'Withdrawn']
Types: ['real', 'text', 'text', 'text', 'text']
Sample row: [34071.0, '601 Squadron', 'Brighton', 'Cannot handle non-empty timestamp argument! 1948', 'Cannot handle non-empty timestamp argument! 1967']
SQL:

assistant: SELECT "Whenbuilt" FROM "Table" WHERE "Builder" = 'Brighton' AND "Withdrawn" = 'September 1964' AND "Name" = 'Blandford Forum';