CREATE TABLE table_27481781_2 (no_in_series VARCHAR, viewers__millions_ VARCHAR)

How many episodes have 18.73 million viewers?
SELECT COUNT(no_in_series) FROM table_27481781_2 WHERE viewers__millions_ = "18.73"
SELECT COUNT("no_in_series") FROM "table_27481781_2" WHERE "18.73" = "viewers__millions_"