CREATE TABLE table_16463 ("No. in season" FLOAT, "No. in series" FLOAT, "Title" TEXT, "Directed by" TEXT, "Written by" TEXT, "Original air date" TEXT, "U.S. viewers  ( million ) " TEXT)

How many millions of U.S. viewers watched the episode that first aired on March 31, 2013?
SELECT "U.S. viewers (million)" FROM table_16463 WHERE "Original air date" = 'March 31, 2013'
SELECT "U.S. viewers (million)" FROM "table_16463" WHERE "Original air date" = 'March 31, 2013'