What was the number of Bitcoins verifiably burned until 2013/4/28?
the number of Bitcoins verifiably burned = max_supply - total_supply; 2013/4/28 refers to date = '2013-04-28'
SELECT T2.max_supply - T2.total_supply FROM coins AS T1 INNER JOIN historical AS T2 ON T1.id = T2.coin_id WHERE T2.date = '2013-04-28' AND T1.name = 'Bitcoin'