CREATE TABLE table_2891 ("No. in series" FLOAT, "No. in season" FLOAT, "Title" TEXT, "Directed by" TEXT, "Written by" TEXT, "U.S. viewers  ( million ) " TEXT, "Original air date" TEXT, "Production code" FLOAT)

What is the series number of the episode that aired March 25, 2010?
SELECT MIN("No. in series") FROM table_2891 WHERE "Original air date" = 'March 25, 2010'
SELECT MIN("No. in series") FROM "table_2891" WHERE "Original air date" = 'March 25, 2010'