Adding Consecutive cells and listing them out

[arvexcel]

List	Sum of 3 consecutive Nos	This is how I want it
2	12	12
3		15
7		15
5	15	9
8
2
2	15
7
6
1	9
3
5

How can i create the third column for the data in Column1 and the input 3 (i.e. 3 consecutive numbers.. i want to add them up in this case).

Thanks

[#2 · Accepted solution]

@arvexcel 

That could be

or

=SUM(INDEX(B:B,(ROW()-ROW($B$3)-1)*3+ROW($B$3)+1):INDEX(B:B,(ROW()-ROW($B$3)-1)*3+ROW($B$3)+3))

[#3]

@Sergei Baklan ur a genius. Thanks

[#4]

@arvexcel , you are welcome