Do not really need a VBA UDF, this should work ona worksheet.

{=SUM(1/FACT(ROW(1:150)))}

or in VBA if thats what you really need

Function test(n As Integer)

Dim s As String
s = "=SUM(1/FACT(ROW(1:" + Trim(Str(n)) + ")))"
test = Evaluate(s)

End Function