Multiply Two Matrices With MMULT Macro

I have two ranges: A1:F1 and A5:A10, 6 elements in each range. When I multiply one by the other I have to enter a formular in some cell (let's say, A14 - we will put the result there): "=MMULT(A1:F1, A5:A10)" and then press Ctrl-Shift-Enter. Very simple.

Question is this: suppose I do not know in advance that I will have 6 elements in each vector, it might be more than 6 or less than six. I will introduce an integer "n", which is the number of elements. Now I have to write a Sub that will perform multiplication. I wrote smth that does not work and I was wondering if someone has ever done this already and can give me a guidance what I am doing wrong. I HAVE ONE CONSTRAINT: I HAVE TO TYPE IN THE FORMULA INTO THE SPREADSHEET VIA VBA (as this will be used further in Solver, which requires formulas to be present in cells).

Y
Sub test()
Dim n
n = 2
Range("A14").Formula = "=MMULT(A1: & Chr(64+n-1)& 1, A5:A & 5+n-1)"
End Sub

I thought it would be equivalent to MMULT(A1:B1, A5:A6).