CREATE TABLE table_22901 ("Series No." FLOAT, "Season No." FLOAT, "Title" CLOB, "Directed by" CLOB, "Written by" CLOB, "Original air date" CLOB, "U.K. viewers  ( million ) " CLOB)

What's the series number of the episode seen by 2.43 million viewers in the UK?
SELECT "Series No." FROM table_22901 WHERE "U.K. viewers (million)" = '2.43'
SELECT "Series No." FROM "table_22901" WHERE "U.K. viewers (million)" = '2.43'