How many celebrities had an 18October2007 Original air Date?
CREATE TABLE "table1_11642945_1" (
  "total_no" real,
  "celebrity" text,
  "director" text,
  "original_air_date" text,
  "viewers" text
);
SELECT COUNT("celebrity") FROM "table1_11642945_1" WHERE "original_air_date"='18October2007';