What is the next number in this sequence?  $$1$$, $$2$$, $$3$$, $$6$$, $$11$$, $$20$$, $$37$$,~\uline{~~~~~~~~~~}~? ． 
Overseas Competition->Knowledge Point->Calculation Modules->Sequences and Number Tables->Patterns in Number Sequences
After the first three numbers, each number is the sum of the previous three numbers. So the next number is $$11 + 20 + 37 = 68$$. 