Which series number had 1.98 million viewers?
CREATE TABLE "table1_22347090_4" (
  "no_in_series" real,
  "no_in_season" real,
  "title" text,
  "directed_by" text,
  "written_by" text,
  "original_air_date" text,
  "production_code" text,
  "u_s_viewers_million" text
);
SELECT MIN("no_in_series") FROM "table1_22347090_4" WHERE "u_s_viewers_million"='1.98';