[excel] How to enter a series of numbers automatically in Excel

Simple Answer:

In A1

=if(b1="","",row()) 

In A2

=if(b2="","",row())  

copy this down the column. Each time an entry is entered in column B the next number in order will be entered in column A.

Suppose you want the answer of 2 in a4 cell because of your heading & other stuff, you can write as

=if(b4="","",row()-2)