Name the number of panelists for 20 january 2006 air date
CREATE TABLE "series_2" (
  "episode_number" real,
  "air_date" text,
  "guest_host" text,
  "musical_guest_song_performed" text,
  "who_knows_the_most_about_the_guest_host_panelists" text
);
SELECT COUNT("who_knows_the_most_about_the_guest_host_panelists") FROM "series_2" WHERE "air_date"='20 January 2006';