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

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'