What should be the last number in the series be?  $$1$$, $$2$$, $$5$$, $$10$$, $$17$$, $$26$$, ． 
Overseas Competition->Knowledge Point->Calculation Modules->Sequences and Number Tables->Patterns in Number Sequences
$$+1$$, $$+3$$, $$+5$$, $$+7$$, $$+9$$, $$+11$$. 