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 A323389 #14 Feb 04 2025 11:36:15
%S A323389 1,2,5,19,88,553,4619,49137,646815,10053183,178725865,3555840644,
%T A323389 78048875298,1871066903575,48617053973267,1360733669185473,
%U A323389 40810827325698897,1305690378666580997,44387116312631271929,1597768080980647428027,60710507893875818581964
%N A323389 The number of connected, unlabeled, undirected, edge-signed cubic graphs (admitting loops and multiedges) on 2n vertices where the degree of the first sign is 2 at each node.
%C A323389 Obtained from the cubic graphs A005967 (connected undirected cubic graphs that may have loops and/or multiedges) by signing each edge with a plus or a minus such that two pluses and one minus meet at each vertex.
%H A323389 Richard J. Mathar, <a href="http://vixra.org/abs/1901.0148">Feynman diagrams of the QED vacuum polarization</a>, vixra:1901.0148 (2019) Section II.
%H A323389 R. J. Mathar, <a href="http://vixra.org/abs/2410.0145">Chord diagrams with directed chords</a>, vixra:2410.0145 (2024) Section Outlook (illustrations)
%o A323389 (PARI) \\ See A339645 for combinatorial species functions.
%o A323389 cycleIndexSeries(n)={1+sLog(sCartProd(sExp(dihedralGroupSeries(n)), sExp(symGroupCycleIndex(2)*x^2 + O(x*x^n))))}
%o A323389 seq(n)={Vec(substpol(OgfSeries(cycleIndexSeries(2*n)), x^2, x))} \\ _Andrew Howroyd_, May 05 2023
%Y A323389 Cf. A005967 (unsigned), A054499 (only one cycle of pluses), A170946 (directed plus-edges).
%K A323389 nonn
%O A323389 0,2
%A A323389 _R. J. Mathar_, Jan 13 2019
%E A323389 Terms a(6) and beyond from _Andrew Howroyd_, May 05 2023