A hobbyist plans to obtain an equivalent resistance of the form R(1+n1) by first connecting n identical resistors of resistance R in parallel and then adding one more resistor R in series with that parallel group. For which of the following target values (expressed in multiples of R) is this design NOT possible with any positive integer n?
(a) 1.25R
(b) 1.75R
(c) 2.00R
(d) 1.50R