Need to add cells depending on other cell.

Hi
I need to add few cells.
But problem is My number of cells depend on other cells value.
E.G
I want to add values from column A
depending on value in cell B2

suppose its B2 is 2
so i will add A1 and A7
suppose b2 is 3
thn I will add A1 A7 and A13 and so on....

Can some one help.?

Thanks in advance

Refered: http://www.excelforum.com/excel-for...ells-depending-on-other-cell.html#post3488332

This has been answered from two other sites: Link in post #1 and also

http://www.mrexcel.com/forum/excel-questions/741514-need-add-cells-depending-other-cell.html