I hava a sheet with more than 1000 rows and the problem is that only
every 13th row contains information I want to have. So I want to
delete the rest of the rows. I have been trying this with

Sub Macro1()

Rows("10:23").Select
Selection.Delete Shift:=xlUp
End Sub

and it works fine but I want to do this automatically. Is there a way
to make the row selection (Rows("10:23") automatical? I tried this
with a counter like
Rows(a & ":" & b) with a and b being values of the counter but it
doesn't work. Any sugestions?