CREATE TABLE table_21486 ("Week" FLOAT, "Date" TEXT, "Opponent" TEXT, "Result" TEXT, "Game site" TEXT, "Record" TEXT, "Attendance" FLOAT)

Of the times the Broncos played the Cincinnati Bengals, what was the highest attendance?
SELECT MAX("Attendance") FROM table_21486 WHERE "Opponent" = 'Cincinnati Bengals'
SELECT MAX("Attendance") FROM "table_21486" WHERE "Opponent" = 'Cincinnati Bengals'