$$1423$$, $$1723$$, $$2123$$,~\uline{~~~~~~~~~~}~, $$3223$$  Which one of the following is the missing number? 
Overseas Competition->Knowledge Point->Calculation Modules->Sequences and Number Tables->Patterns in Number Sequences
The sequence increases in this order: $$300$$, $$400$$, $$500$$, $$600$$, $$\dots$$ 