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 A003089 M1417 #36 Feb 16 2025 08:32:27
%S A003089 1,1,2,5,12,30,79,227,710,2322,8071,29503,112822,450141,1867871,
%T A003089 8037472,35787667,164551477,779945969,3804967442,19079312775,
%U A003089 98211456209,518397621443,2802993986619,15510781288250,87765472487659,507395402140211,2994893000122118,18035546081743772,110741792670074054,692894304050453139
%N A003089 Number of connected line graphs with n nodes.
%C A003089 Sequence is identical to the number of connected graphs on n edges (A002905), except for the term a(3). The three connected 3-edge graphs (P_4, K_3 and K_{1,3}) yield only two linegraphs because K_3 and K_{1,3} have isomorphic linegraphs. No other connected nonisomorphic graphs have isomorphic linegraphs.
%D A003089 F. Harary and E. M. Palmer, Graphical Enumeration, Academic Press, NY, 1973, p. 221.
%D A003089 R. C. Read and R. J. Wilson, An Atlas of Graphs, Oxford, 1998.
%D A003089 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
%H A003089 Max Alekseyev, <a href="/A003089/b003089.txt">Table of n, a(n) for n = 1..60</a>
%H A003089 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/LineGraph.html">Line Graph</a>.
%Y A003089 Cf. A002905.
%K A003089 nonn,nice
%O A003089 1,3
%A A003089 _N. J. A. Sloane_
%E A003089 More terms from Ronald C. Read.
%E A003089 More terms from _Gordon F. Royle_, Jun 05 2003
%E A003089 a(25)-a(26) from _Max Alekseyev_, Nov 25 2013
%E A003089 a(27) and beyond from _Max Alekseyev_, Sep 07 2016