Hello, I'm trying to sum certain cells in macro, however, the cell range is
not fixed;(i.e cells are based on variables)

Herebelow is an example of the macro but it's giving an error at the sum
funtion (would appreciate if you could help me find the mistake):

Sub R()
Dim i As Integer, x As Integer, y As Integer, z As Integer

For i = 2 To 15
y = i - z
x = i - 1
Cells(i, "H").Formula = "=Sum(Cells(y, "H"), Cells(x, "H"))"
z = 0
y = 0
x = 0
Next i
End Sub

Thank you