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A051045
Number of distinct resistances possible for n resistors with resistances 1, 2, ..., n, each connected in series or parallel to the previous one.
For n = 4, there would be an additional 4 possible values if circuits were allowed that combine complex subcircuits in series or parallel, rather than requiring that one of them consists of a single resistor. See illustration in links. - Kival Ngaokrajang, Aug 22 2013 (rephrased by Dave R.M. Langers, Nov 13 2013)