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%I M1417 #35 Feb 27 2023 16:07:29
%S 1,1,2,5,12,30,79,227,710,2322,8071,29503,112822,450141,1867871,
%T 8037472,35787667,164551477,779945969,3804967442,19079312775,
%U 98211456209,518397621443,2802993986619,15510781288250,87765472487659,507395402140211,2994893000122118,18035546081743772,110741792670074054,692894304050453139
%N Number of connected line graphs with n nodes.
%C 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 F. Harary and E. M. Palmer, Graphical Enumeration, Academic Press, NY, 1973, p. 221.
%D R. C. Read and R. J. Wilson, An Atlas of Graphs, Oxford, 1998.
%D N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
%H Max Alekseyev, <a href="/A003089/b003089.txt">Table of n, a(n) for n = 1..60</a>
%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/LineGraph.html">Line Graph</a>.
%Y Cf. A002905.
%K nonn,nice
%O 1,3
%A _N. J. A. Sloane_
%E More terms from Ronald C. Read.
%E More terms from _Gordon F. Royle_, Jun 05 2003
%E a(25)-a(26) from _Max Alekseyev_, Nov 25 2013
%E a(27) and beyond from _Max Alekseyev_, Sep 07 2016
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