This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A123750 #17 Aug 09 2018 04:26:56 %S A123750 1,4,17,94,667,5752,58053,669970,8698991,125499820,1991637529, %T A123750 34479906886,646671878595,13061304372448,282652185684845, %U A123750 6524494505342842,160018549741811479,4155443426929596436,113905714869793400001,3286624199431263921838 %N A123750 Number of distinct resistances possible with at most n arbitrary resistors connected in series or in parallel. %C A123750 The difference between this problem and A005840 and A051045 is the word "at most". In this problem, at most n different resistors are used to generate all possible resistances using in series and in parallel wirings, also including resistances where some of the resistors from the collection 1,2,...,n, are not used. %F A123750 a(n) = 2 * A005840(n) + n - 2, n > 1. %F A123750 E.g.f.: exp(x)*(-2*exp(x) + exp(x)*x + 2)/(-2 + exp(x)). %p A123750 a:= n-> n!* coeff(series(exp(x)*(-2*exp(x) + %p A123750 exp(x)*x + 2)/(-2 + exp(x)), x, n+1),x,n): %p A123750 seq(a(n), n=1..25); %Y A123750 Cf. A005840, A051045. %K A123750 nonn,uned %O A123750 1,2 %A A123750 I. N. Galidakis (jgal(AT)ath.forthnet.gr), Nov 28 2006