DSym

Public Enum DimSize
    minRow = 5 ' Start Row point
    maxRow = 20 ' End Row point
End Enum

Sub Idea()
Dim c As Long ' Column ref
Dim r As Long ' Row ref
Dim ColArr() As Variant

ColArr = Array(11, 13) ' columns K and M, you can add more as neceassry

For r = DimSize.minRow To DimSize.maxRow
    For c = LBound(ColArr) To UBound(ColArr)
        Debug.Print Cells(r, ColArr(c)).Address ' line to test your array
        ' insert your action code here
    Next c
Next r

End Sub