其它
What is the missing number in the sequence below?  1, 3, 7, 15, 31,~\uline{~~~~~~~~~~}~ 
Overseas Competition->Knowledge Point->Combinatorics->Patterns of Figures
1, 3, 7, 15, 31, \cdots ..  2. 4. 8.~ 16.~ 32  31+32 = 64 