what is the total number o production code where us viewers is 2.76?
CREATE TABLE "table1_21726793_1" (
  "no" real,
  "title" text,
  "directed_by" text,
  "written_by" text,
  "original_air_date" text,
  "production_code" text,
  "u_s_viewers_million" text
);
SELECT COUNT("production_code") FROM "table1_21726793_1" WHERE "u_s_viewers_million"='2.76';