1, 3, 7, 15, 31, \cdots ..  2. 4. 8.~ 16.~ 32  31+32 = 64 
What is the missing number in the sequence below?  $1, 3, 7, 15, 31,$~\uline{~~~~~~~~~~}~ 
  - $$63$$ 
  - $$47$$ 
  - $$57$$ 
  - $$59$$ 
  - None of the above 